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Sunday, May 28, 2023

Slavery in the colonial history of the United States

Enslaved populations in the Thirteen Colonies in 1770

Slavery in the colonial history of the United States, from 1526 to 1776, developed from complex factors, and researchers have proposed several theories to explain the development of the institution of slavery and of the slave trade. Slavery strongly correlated with the European colonies' demand for labor, especially for the labor-intensive plantation economies of the sugar colonies in the Caribbean and South America, operated by Great Britain, France, Spain, Portugal, and the Dutch Republic.

Slave-ships of the Atlantic slave trade transported captives for slavery from Africa to the Americas. Indigenous people were also enslaved in the North American colonies, but on a smaller scale, and Indian slavery largely ended in the late eighteenth century. Enslavement of Indigenous people did continue to occur in the Southern states until the Emancipation Proclamation issued by President Abraham Lincoln in 1863. Slavery was also used as a punishment for crimes committed by free people. In the colonies, slave status for Africans became hereditary with the adoption and application of civil law into colonial law, which defined the status of children born in the colonies as determined by the mother - known as partus sequitur ventrem. Children born to enslaved women were born enslaved, regardless of paternity. Children born to free women were free, regardless of ethnicity. By the time of the American Revolution, the European colonial powers had embedded chattel slavery for Africans and their descendants throughout the Americas, including the future United States.

Native Americans

The massacre of the Pequots resulted in the enslavement of some of the survivors by English colonists.
 
A 1711 Petition of Sarah Robins, a "free born Indian woman", to Governor Robert Hunter of New York, protesting her threat of enslavement for refusal to convert to Christianity

Native Americans enslaved members of their own and other tribes, usually as a result of taking captives in raids and warfare, both before and after Europeans arrived. This practice continued into the 1800s. In some cases, especially for young women or children, Native American families adopted captives to replace members they had lost. Enslavement was not necessarily hereditary. Slaves included captives from wars and slave raids; captives bartered from other tribes, sometimes at great distances; children sold by their parents during famines; and men and women who staked themselves in gambling when they had nothing else, which put them into servitude in some cases for life.

In three expeditions between 1514 and 1525, Spanish explorers visited the Carolinas and enslaved Native Americans, who they took to their base on Santo Domingo. The Spanish crown's charter for its 1526 colony in the Carolinas and Georgia was more restrictive. It required that Native Americans be treated well, paid, and converted to Christianity, but it also allowed already enslaved Native Americans to be bought and exported to the Caribbean if they had been enslaved by other Native Americans. This colony did not survive, so it is not clear if it exported any slaves. Native Americans were enslaved by the Spanish in Florida under the encomienda system. New England and the Carolinas captured Native Americans in wars and distributed them as slaves.

Native Americans captured and enslaved some early European explorers and colonists.

Larger societies structured as chiefdoms kept slaves as unpaid field laborers. In band societies, owning enslaved captives attested to the captor's military prowess. Some war captives were subjected to ritualized torture and execution. Alan Gallay and other historians emphasize differences between Native American enslavement of war captives and the European slave trading system, into which numerous native peoples were integrated. Richard White, in The Middle Ground, elucidates the complex social relationships between Native American groups and the early empires, including 'slave' culture and scalping. Robbie Ethridge states,

Let there be no doubt...that the commercial trade in Indian slaves was not a continuation and adaptation of pre-existing captivity patterns. It was a new kind of slave, requiring a new kind of occupational specialty ... organized militaristic slavers.

One example of militaristic slaving can be seen in Nathaniel Bacon's actions in Virginia during the late 1670s. In June 1676, the Virginia assembly granted Bacon and his men what equated to a slave-hunting license by providing that any enemy Native Americans caught were to be slaves for life. They also provided soldiers who had captured Native Americans with the right to "reteyne and keepe all such Indian slaves or other Indian goods as they either have taken or hereafter shall take." By this order, the assembly had made a public decision to enslave Native Americans. In the years to follow, other laws resulted in Native Americans being grouped with other non-Christian servants who had imported to the colonies (Negro slaves) as slaves for life.

Puritan New England, Virginia, Spanish Florida, and the Carolina colonies engaged in large-scale enslavement of Native Americans, often through the use of Indian proxies to wage war and acquire the slaves. In New England, slave raiding accompanied the Pequot War and King Philip's War but declined after the latter war ended in 1676. Enslaved Native Americans were in Jamestown from the early years of the settlement, but large-scale cooperation between English slavers and the West and Occaneechi peoples, whom they armed with guns, did not begin until the 1640s. These groups conducted enslaving raids in what is now Georgia, Tennessee, North Carolina, South Carolina, Florida, and possibly Alabama. The Carolina slave trade, which included both trading and direct raids by colonists, was the largest among the British colonies in North America, estimated at 24,000 to 51,000 Native Americans by Gallay.

Historian Ulrich Phillips argues that Africans were inculcated as slaves and the best answer to the labor shortage in the New World because Native American slaves were more familiar with the environment, and would often successfully escape into the frontier territory they knew. Africans had more difficulty surviving in unknown territory. Africans were also more familiar with large scale indigo and rice cultivation, of which Native Americans were unfamiliar. The early colonial America depended heavily on rice and indigo cultivation producing disease-carrying mosquitoes caused malaria, a disease the Africans were far less susceptible to than Native American slaves.

The first enslaved Africans

Carolinas

The first African slaves in what would become the present-day United States of America arrived in Puerto Rico in the early 16th century, at the hands of the Portuguese. The island's native population was conquered by the Spanish settler Juan Ponce de León with the help of a free West African conquistador, Juan Garrido, by 1511. The slave population on the island grew after the Spanish crown granted import rights to its citizens, but did not reach its peak until the 18th century.

African slaves arrived on August 9, 1526, in Winyah Bay (off the coast of present-day South Carolina) with a Spanish expedition. Lucas Vázquez de Ayllón brought 600 colonists to start a colony at San Miguel de Gualdape. Records say the colonists included enslaved Africans, without saying how many. After a month Ayllón moved the colony to what is now Georgia.

Until the early 18th century, enslaved Africans were difficult to acquire in the British mainland colonies. Most were sold from Africa to the West Indies for the labor-intensive sugar trade. The large plantations and high mortality rates required continued importation of slaves. One of the first major centers of African slavery in the English North American colonies occurred with the founding of Charles Town and the Province of Carolina in 1670. The colony was founded mainly by sugar planters from Barbados, who brought relatively large numbers of African slaves from that island to develop new plantations in the Carolinas.

To meet agricultural labor needs, colonists also practiced Indian slavery for some time. The Carolinians transformed the Indian slave trade during the late 17th and early 18th centuries by treating such slaves as a trade commodity to be exported, mainly to the West Indies. Historian Alan Gallay estimates that between 1670 and 1715, an estimated 24,000 to 51,000 captive Native Americans were exported from South Carolina to the Caribbean. This was a much higher number than the number of Africans imported to the English mainland colonies during the same period.

Georgia

The first African slaves in what is now Georgia arrived in mid-September 1526 with Lucas Vázquez de Ayllón's establishment of San Miguel de Gualdape on the current Georgia coast. They rebelled and lived with indigenous people, destroying the colony in less than 2 months.

Two centuries later, Georgia was the last of the Thirteen Colonies to be established and the furthest south (Florida was not one of the Thirteen Colonies). Founded in the 1730s, Georgia's powerful backers did not object to slavery as an institution, but their business model was to rely on labor from Britain (primarily England's poor) and they were also concerned with security, given the closeness of then Spanish Florida, and Spain's regular offers to enemy-slaves to revolt or escape. Despite agitation for slavery, it was not until a defeat of the Spanish by Georgia colonials in the 1740s that arguments for opening the colony to slavery intensified. To staff the rice plantations and settlements, Georgia's proprietors relented in 1751, and African slavery grew quickly. After becoming a royal colony, in the 1760s Georgia began importing slaves directly from Africa.

Florida

One African slave, Estevanico arrived with the Narváez expedition in Tampa Bay in April 1528 and marched north with the expedition until September, when they embarked on rafts from the Wakulla River, heading for Mexico. African slaves arrived again in Florida in 1539 with Hernando de Soto, and in the 1565 founding of St. Augustine, Florida. When St. Augustine was founded in 1565, the site already had enslaved Native Americans, whose ancestors had migrated from Cuba. The Spanish settlement was sparse and they held comparatively few slaves.

The Spanish promised freedom to refugee slaves from the English colonies of South Carolina and Georgia in order to destabilize English settlement. If the slaves converted to Catholicism and agreed to serve in a militia for Spain, they could become Spanish citizens. By 1730 the black settlement known as Fort Mose developed near St. Augustine and was later fortified. There were two known Fort Mose sites in the eighteenth century, and the men helped defend St. Augustine against the British. It is "the only known free black town in the present-day southern United States that a European colonial government-sponsored. The Fort Mose Site, today a National Historic Landmark, is the location of the second Fort Mose." During the nineteenth century, this site became marsh and wetlands.

In 1763, Great Britain took over Florida in an exchange with Spain after defeating France in the Seven Years' War. Spain evacuated its citizens from St. Augustine, including the residents of Fort Mose, transporting them to Cuba. As Britain developed the colony for plantation agriculture, the percentage of slaves in the population in twenty years rose from 18% to almost 65% by 1783.

Texas and the southwest

An African slave, Estevanico, reached Galveston island in November 1528, with the remnants of the Narváez expedition in Florida. The group headed south on the mainland in 1529, trying to reach Spanish settlements. They were captured and held by Native Americans until 1535. They traveled northwest to the Pacific Coast, then south along the coast to San Miguel de Culiacán, which had been founded in 1531, and then to Mexico City.

Spanish Texas had few African slaves, but the colonists enslaved many Native Americans. Beginning in 1803, Spain freed slaves who escaped from the Louisiana territory, recently acquired by the United States. More African-descended slaves were brought to Texas by American settlers.

Virginia and Chesapeake Bay

The first recorded Africans in Virginia arrived in late August 1619. The White Lion, a privateer ship owned by Robert Rich, 2nd Earl of Warwick but flying a Dutch flag, docked at what is now Old Point Comfort (located in modern-day Hampton) with approximately 20 Africans. They were captives from the area of present-day Angola and had been seized by the British crew from a Portuguese slave ship, the "São João Bautista". To obtain the Africans, the Jamestown colony traded provisions with the ship. Some number of these individuals appear to have been treated like indentured servants, since slave laws were not passed until later, in 1641 in Massachusetts and in 1661 in Virginia. But from the beginning, in accordance with the custom of the Atlantic slave trade, most of this relatively small group, appear to have been treated as slaves, with "African" or "negro" becoming synonymous with "slave". Virginia enacted laws concerning runaway slaves and 'negroes' in 1672.

Some number of the colony's early Africans earned freedom by fulfilling a work contract or for converting to Christianity. At least one of these, Anthony Johnson, in turn, acquired slaves or indentured servants for workers himself. Historians such as Edmund Morgan say this evidence suggests that racial attitudes were much more flexible in early 17th-century Virginia than they would later become. A 1625 census recorded 23 Africans in Virginia. In 1649 there were 300, and in 1690 there were 950. Over this period, legal distinctions between white indentured servants and "Negros" widened into lifelong and inheritable chattel-slavery for Africans and people of African descent.

New England

The 1677 work The Doings and Sufferings of the Christian Indians documents English colonial prisoners of war (not, in fact, opposing combatants, but imprisoned members of English-allied forces) being enslaved and sent to Caribbean destinations in the aftermath of Metacom's War. Captive indigenous opponents, including women and children, were also sold into slavery at a substantial profit, to be transported to West Indies colonies.

African and Native American slaves made up a smaller part of the New England economy, which was based on yeoman farming and trades, than in the South, and a smaller fraction of the population, but they were present. Most were house servants, but some worked at farm labor. The Puritans codified slavery in 1641. The Massachusetts Bay royal colony passed the Body of Liberties, which prohibited slavery in some instances, but did allow three legal bases of slavery. Slaves could be held if they were captives of war, if they sold themselves into slavery, were purchased from elsewhere, or if they were sentenced to slavery by the governing authority. The Body of Liberties used the word "strangers" to refer to people bought and sold as slaves, as they were generally not native born English subjects. Colonists came to equate this term with Native Americans and Africans.

The New Hampshire Assembly in 1714 passed "An Act To Prevent Disorders In The Night", prefiguring the development of sundown towns in the United States:

Whereas great disorders, insolencies and burglaries are oft times raised and committed in the night time by Indian, Negro, and Molatto Servants and Slaves to the Disquiet and hurt of her Majesty, No Indian, Negro, or Molatto is to be from Home after 9 o'clock.

Notices emphasizing and re-affirming the curfew were published in The New Hampshire Gazette in 1764 and 1771.

New York and New Jersey

The Dutch West India Company introduced slavery in 1625 with the importation of eleven enslaved blacks who worked as farmers, fur traders, and builders to New Amsterdam (present day New York City), capital of the nascent province of New Netherland. The Dutch colony expanded across the North River (Hudson River) to Bergen (in today's New Jersey). Later, slaves were also held privately by settlers in the area. Although enslaved, the Africans had a few basic rights and families were usually kept intact. They were admitted to the Dutch Reformed Church and married by its ministers, and their children could be baptized. Slaves could testify in court, sign legal documents, and bring civil actions against whites. Some were permitted to work after hours earning wages equal to those paid to white workers. When the colony fell to the English in the 1660s, the company freed all its slaves, which created an early nucleus of free Negros in the area.

The English continued to import more slaves. Enslaved Africans performed a wide variety of skilled and unskilled jobs, mostly in the burgeoning port city and surrounding agricultural areas. In 1703 more than 42% of New York City's households held slaves, a percentage higher than in the cities of Boston and Philadelphia, and second only to Charleston in the South.

Midwest, Mississippi River, and Louisiana

The French introduced legalized slavery into their colonies in New France both near the Great Lakes and the Mississippi River. They also used slave labor on their island colonies in the Caribbean: Guadeloupe and especially Saint-Domingue. After the port of New Orleans was founded in 1718 with access to the Gulf Coast, French colonists imported more African slaves to the Illinois Country for use as agricultural or mining laborers. By the mid-eighteenth century, slaves accounted for as much as one-third of the limited population in that rural area.

Slavery was much more extensive in lower colonial Louisiana, where the French developed sugar cane plantations along the Mississippi River. Slavery was maintained during the French (1699–1763, and 1800–1803) and Spanish (1763–1800) periods of government. The first people enslaved by the French were Native Americans, but they could easily escape into the countryside which they knew well. Beginning in the early 18th century, the French imported Africans as laborers in their efforts to develop the colony. Mortality rates were high for both colonists and Africans, and new workers had to be regularly imported.

Implemented in colonial Louisiana in 1724, Louis XIV of France's Code Noir regulated the slave trade and the institution of slavery in the French colonies. As a result, Louisiana and the Mobile, Alabama areas developed very different patterns of slavery compared to the British colonies.

As written, the Code Noir gave some rights to slaves, including the right to marry. Although it authorized and codified cruel corporal punishment against slaves under certain conditions, it forbade slave owners to torture slaves, to separate married couples, and to separate young children from their mothers. It required owners to instruct slaves in the Catholic faith, implying that Africans were human beings endowed with a soul, an idea that had not been acknowledged until then.

The Code Noir forbade interracial marriages, but interracial relationships were formed in La Louisiane from the earliest years. In New Orleans society particularly, a formal system of concubinage, known as plaçage, developed. Usually formed between young white men and African or African-American women, these relationships were formalized with contracts that sometimes provided for freedom for a woman and her children (if she was still enslaved), education for the mixed-race children of the union, especially boys; and sometimes a property settlement. Free people of color became an intermediate social caste between whites and enslaved blacks; many practiced artisan trades, and some acquired educations and property. Some white fathers sent their mixed-race sons to France for education in military schools.

Gradually in the English colonies, slavery became known as a racial caste system that generally encompassed all people of African descent, including those of mixed race. From 1662, Virginia defined social status by the status of the mother, unlike in England, where under common law fathers determined the status of their children, whether legitimate or natural. Thus, under the doctrine of partus sequitur ventrum, children born to enslaved mothers were considered slaves, regardless of their paternity. Similarly, children born to mothers who were free were also free, whether or not of mixed-race. At one time, Virginia had prohibited enslavement of Christian individuals, but lifted that restriction with its 1662 law. In the 19th century, laws were passed to restrict the rights of free people of color and mixed-race people (sometimes referred to as mulattoes) after early slave revolts. During the centuries of slavery in the British colonies, the number of mixed-race slaves increased.

Slave rebellions

Colonial slave rebellions before 1776, or before 1801 for Louisiana, include:

16th century

While the British knew about Spanish and Portuguese slave trading, they did not implement slave labor in the Americas until the 17th century. British travelers were fascinated by the dark-skinned people they found in West Africa; they developed mythologies that situated them in their view of the cosmos.

The first Africans to arrive in England came voluntarily in 1555 with John Lok (an ancestor of the famous philosopher John Locke). Lok intended to teach them English in order to facilitate the trading of material goods with West Africa. This model gave way to a slave trade initiated by John Hawkins, who captured 300 Africans and sold them to the Spanish. Blacks in England were subordinate but never had the legal status of chattel slaves.

In 1607, England established Jamestown as its first permanent colony on the North American continent. Tobacco became the chief commodity crop of the colony, due to the efforts of John Rolfe in 1611. Once it became clear that tobacco was going to drive the Jamestown economy, more workers were needed for the labor-intensive crop. British plantation owners in North America and the Caribbean also needed a workforce for their cash crop plantations, which was initially filled by indentured servants from Britain before transitioning to Native American and West African slave labor. During this period, the English established colonies in Barbados in 1624 and Jamaica in 1655. These and other Caribbean colonies generated wealth by the production of sugar cane, as sugar was in high demand in Europe. They also were an early center of the slave trade for the growing English colonial empire.

English colonists entertained two lines of thought simultaneously toward indigenous Native Americans. Because these people were lighter-skinned, they were seen as more European and therefore as candidates for civilization. At the same time, because they were occupying the land desired by colonists, they were from the beginning, frequent targets of colonial violence.

At first, indentured servants were used for labor. These servants provided up to seven years of service in exchange for having their trip to Jamestown paid for by someone in Jamestown. The person who paid was granted additional land in headrights, dependent on how many persons he paid to travel to the colony. Once the seven years were over, the indentured servant who survived was free to live in Jamestown as a regular citizen. However, colonists began to see indentured servants as too costly, in part because the high mortality rate meant the force had to be resupplied. In addition, an improving economy in England reduced the number of persons who were willing to sign up as indentured servants for the harsh conditions in the colonies.

17th century

In 1619, an English Privateer, The White Lion, with Dutch letters of marque, brought African slaves pillaged from a Portuguese slave ship to Point Comfort.

Several colonial colleges held enslaved people as workers and relied on them to operate.[85]

The development of slavery in 17th-century America

The First Slave Auction at New Amsterdam in 1655, an illustration by Howard Pyle

The laws relating to slavery and their enforcement hardened in the second half of the 17th century, and the prospects for Africans and their descendants grew increasingly dim. By 1640, the Virginia courts had sentenced at least one black servant, John Punch, to slavery. In 1656 Elizabeth Key won a suit for freedom based on her father's status as a free Englishman, his having baptized her as Christian in the Church of England, and the fact that he established a guardianship for her that was supposed to be a limited indenture. Following her case, in 1662 the Virginia House of Burgesses passed a law with the doctrine of partus, stating that any child born in the colony would follow the status of its mother, bond or free. This overturned a long held principle of English Common Law, whereby a child's status followed that of the father. It removed any responsibility for the children from white fathers who had abused and raped slave women. Most did not acknowledge, support, or emancipate their resulting children.

During the second half of the 17th century, the British economy improved and the supply of British indentured servants declined, as poor Britons had better economic opportunities at home. At the same time, Bacon's Rebellion of 1676 led planters to worry about the prospective dangers of creating a large class of restless, landless, and relatively poor white men (most of them former indentured servants). Wealthy Virginia and Maryland planters began to buy slaves in preference to indentured servants during the 1660s and 1670s, and poorer planters followed suit by c.1700. (Slaves cost more than servants, so initially only the wealthy could invest in slaves.) The first British colonists in Carolina introduced African slavery into the colony in 1670, the year the colony was founded, and Charleston ultimately became the busiest slave port in North America. Slavery spread from the South Carolina Lowcountry first to Georgia, then across the Deep South as Virginia's influence had crossed the Appalachians to Kentucky and Tennessee. Northerners also purchased slaves, though on a much smaller scale. Enslaved people outnumbered free whites in South Carolina from the early 1700s to the Civil War. An authoritarian political culture evolved to prevent slave rebellion and justify white slaveholding. Northern slaves typically dwelled in towns, rather than on plantations as in the South, and worked as artisans and artisans' assistants, sailors and longshoremen, and domestic servants.

In 1672, King Charles II rechartered the Royal African Company (it had initially been set up in 1660), as an English monopoly for the African slave and commodities trade—thereafter in 1698, by statute, the English parliament opened the trade to all English subjects. The slave trade to the mid-Atlantic colonies increased substantially in the 1680s, and by 1710 the African population in Virginia had increased to 23,100 (42% of total); Maryland contained 8,000 Africans (23% of total). In the early 18th century, England passed Spain and Portugal to become the world's leading slave-trader.

The North American royal colonies not only imported Africans but also captured Native Americans, impressing them into slavery. Many Native Americans were shipped as slaves to the Caribbean. Many of these slaves from the British colonies were able to escape by heading south, to the Spanish colony of Florida. There they were given their freedom if they declared their allegiance to the King of Spain and accepted the Catholic Church. In 1739 Fort Mose was established by African-American freedmen and became the northern defense post for St. Augustine. In 1740, English forces attacked and destroyed the fort, which was rebuilt in 1752. Because Fort Mose became a haven for escaped slaves from the English colonies to the north, it is considered a precursor site of the Underground Railroad.

Chattel slavery developed in British North America before the full legal apparatus that supported slavery did. During the late 17th century and early 18th century, harsh new slave codes limited the rights of African slaves and cut off their avenues to freedom. The first full-scale slave code in British North America was South Carolina's (1696), which was modeled on the colonial Barbados slave code of 1661. It was updated and expanded regularly throughout the 18th century.

A 1691 Virginia law prohibited slaveholders from emancipating slaves unless they paid for the freedmen's transportation out of Virginia. Virginia criminalized interracial marriage in 1691, and subsequent laws abolished free blacks' rights to vote, hold office, and bear arms. Virginia's House of Burgesses established the basic legal framework for slavery in 1705.

The Atlantic slave trade to North America

Of the enslaved Africans brought to the New World an estimated 5–7% ended up in British North America. The vast majority of slaves transported across the Atlantic Ocean were sent to the Caribbean sugar colonies, Brazil, or Spanish America. Throughout the Americas, but especially in the Caribbean, tropical disease took a large toll on their population and required large numbers of replacements. Many Africans had limited natural immunity to yellow fever and malaria; but malnutrition, poor housing, inadequate clothing allowances, and overwork contributed to a high mortality rate.

In British North America the slave population rapidly increased via the birth rate, whereas in the Caribbean colonies they did not. The lack of proper nourishment, being suppressed sexually, and poor health are possible reasons. Of the small numbers of babies born to slaves in the Caribbean, only about 1/4 survived the miserable conditions on sugar plantations.

It was not only the major colonial powers of Western Europe such as France, England, Spain, Portugal, and the Netherlands that were involved. Other countries, including Sweden and Denmark, participated in the trans-Atlantic slave trade though on a much more limited scale.

Sexual role differentiation and slavery

"Depending upon their age and gender, slaves were assigned a particular task, or tasks, that had to be completed during the course of the day." In certain settings, men would participate in the hard labor, such as working on the farm, while women would generally work in the household. They would "be sent out on errands but in most cases their jobs required that they spend much of their time within their owner's household." These gender distinctions were mainly applied in the Northern colonies and on larger plantations. In Southern colonies and smaller farms, however, women and men typically engaged in the same roles, both working in the tobacco crop fields for example.

Although slave women and men in some areas performed the same type of day-to-day work, "[t]he female slave ... was faced with the prospect of being forced into sexual relationships for the purpose of reproduction." This reproduction would either be forced between one African slave and another, or between the slave woman and the owner. Slave owners saw slave women in terms of prospective fertility. That way, the number of slaves on a plantation could multiply without having to purchase another African. Unlike the patriarchal society of white Anglo-American colonists, "slave families" were more matriarchal in practice. "Masters believed that slave mothers, like white women, had a natural bond with their children that therefore it was their responsibility—more so than that of slave fathers—to care for their offspring." Therefore, women had the extra responsibility, on top of their other day-to-day work, to take care of children. Men, in turn, were often separated from their families. "At the same time that slaveholders promoted a strong bond between slave mothers and their children, they denied to slave fathers their paternal rights of ownership and authority..." Biological families were often separated by sale.

Indentured servitude

Some historians such as Edmund Morgan and Lerone Bennett have suggested that indentured servitude provided a model for slavery in the 17th-century Crown Colonies. In practice, indentured servants were teenagers in England whose fathers sold their labor voluntarily for a period of time (typically four to seven years), in return for free passage to the colonies, room and board and clothes, and training in an occupation. After that, they received cash, clothing, tools, and/or land, and became ordinary settlers.

The Quaker petition against slavery

In 1688, four German Quakers in Germantown, a town outside Philadelphia, wrote a petition against the use of slaves by English colonists in the nearby countryside. They presented the petition to their local Quaker Meeting, and the Meeting was sympathetic, but could not decide what the appropriate response should be. The Meeting passed the petition up the chain of authority to Philadelphia Yearly Meeting, where it continued to be ignored. It was archived and forgotten for 150 years.

The Quaker petition was the first public American document of its kind to protest slavery. It was also one of the first public declarations of universal human rights. While the petition was forgotten for a time, the idea that every human has equal rights was regularly discussed in Philadelphia Quaker society through the eighteenth century.

18th century

During the Great Awakening of the late eighteenth century, Methodist and Baptist preachers toured in the South, trying to persuade planters to manumit their slaves on the basis of equality in God's eyes. They also accepted slaves as members and preachers of new chapels and churches. The first black churches (all Baptist) in what became the United States were founded by slaves and free blacks in Aiken County, South Carolina, in 1773; Petersburg, Virginia, in 1774; and Savannah, Georgia, in 1778, before the end of the Revolutionary War.

Slavery was officially recognized as a serious offense in 1776 by the Philadelphia Yearly Meeting. The Yearly Meeting had been against slavery since the 1750s.

East Indian slaves

In the early 21st century, new research has revealed that small numbers of East Indians were brought to the colonies as enslaved laborers, during the period when both India and the colonies were under British control. As an example, an ad in the Virginia Gazette of August 4, 1768, describes one young "East Indian" as "a well made fellow, about 5 feet 4 inches high" who had "a thin visage, a very sly look, and a remarkable set of fine white teeth." Another slave is identified as "an East India negro man" who speaks French and English. Most of the Indian slaves were already converted to Christianity, were fluent in English, and took western names. Their original names and homes are not known. Their descendants have mostly merged with the African-American community, which also incorporated European ancestors. Today, descendants of such East Indian slaves may have a small percent of DNA from Asian ancestors but it likely falls below the detectable levels for today's DNA tests, as most of the generations since would have been primarily of ethnic African and European ancestry.

Beginning of the anti-slavery movement

African and African-American slaves expressed their opposition to slavery through armed uprisings such as the Stono Rebellion (1739) in South Carolina. More typically, they resisted through work slowdowns, tool-breaking, and running away, either for short periods or permanently. Until the Revolutionary era, almost no white American colonists spoke out against slavery. Even the Quakers generally tolerated slaveholding (and slave-trading) until the mid-18th century, although they emerged as vocal opponents of slavery in the Revolutionary era. During the Great Awakening, Baptist and Methodist preachers in the South originally urged planters to free their slaves. In the nineteenth century, they more often urged better treatment of slaves.

Further events

Late 18th and 19th century

During and following the Revolution, the northern states all abolished slavery, with New Jersey acting last in 1804. Some of these state jurisdictions enacted the first abolition laws in the entire New World. In states that passed gradual abolition laws, such as New York and New Jersey, children born to slave mothers had to serve an extended period of indenture into young adulthood. In other cases, some slaves were reclassified as indentured servants, effectively preserving the institution of slavery through another name.

Often citing Revolutionary ideals, some slaveholders freed their slaves in the first two decades after independence, either outright or through their wills. The proportion of free blacks rose markedly in the Upper South in this period, before the invention of the cotton gin created a new demand for slaves in the developing "Cotton Kingdom" of the Deep South.

By 1808 (the first year allowed by the Constitution to federally ban the import slave trade), all states (except South Carolina) had banned the international buying or selling of slaves. Acting on the advice of President Thomas Jefferson, who denounced the international trade as "violations of human rights which have been so long continued on the unoffending inhabitants of Africa, in which the morality, the reputation, and the best interests of our country have long been eager to proscribe", in 1807 Congress also banned the international slave trade. However, the domestic slave trade continued in the South. It brought great wealth to the South, especially to New Orleans, which became the fourth largest city in the country, also based on the growth of its port. In the antebellum years, more than one million enslaved African Americans were transported from the Upper South to the developing Deep South, mostly in the slave trade. Cotton culture, dependent on slavery, formed the basis of new wealth in the Deep South.

In 1844 the Quaker petition was rediscovered and became a focus of the burgeoning abolitionist movement.

Emancipation Proclamation and end of slavery in the US

On 1 January 1863, Abraham Lincoln signed Emancipation Proclamation freeing slaves in areas in rebellion during the American Civil War when Union troops advanced south. The Thirteenth Amendment (abolition of slavery and involuntary servitude) was ratified in December 1865.

Slavery in contemporary Africa

The continent of Africa is one of the regions most rife with contemporary slavery. Slavery in Africa has a long history, within Africa since before historical records, but intensifying with the trans-Saharan and Indian Ocean slave trade and again with the trans-Atlantic slave trade; the demand for slaves created an entire series of kingdoms (such as the Ashanti Empire) which existed in a state of perpetual warfare in order to generate the prisoners of war necessary for the lucrative export of slaves. These patterns persisted into the colonial period during the late 19th and early 20th century. Although the colonial authorities attempted to suppress slavery from about 1900, this had very limited success, and after decolonization, slavery continues in many parts of Africa despite being technically illegal.

Slavery in the Sahel region (and to a lesser extent the Horn of Africa) exists along the racial and cultural boundary of Arabized Berbers in the north and darker Africans in the south. Slavery in the Sahel states of Mauritania, Mali, Niger, Chad and Sudan in particular, continues a centuries-old pattern of hereditary servitude. Other forms of traditional slavery exist in parts of Ghana, Benin, Togo and Nigeria. There are other, non-traditional forms of slavery in Africa today, mostly involving human trafficking and the enslavement of child soldiers and child labourers, e.g. human trafficking in Angola, and human trafficking of children from Togo, Benin and Nigeria to Gabon and Cameroon.

Modern day slavery in Africa according to the Anti-Slavery Society includes exploitation of subjugate populations even when their condition is not technically called "slavery":

Although this exploitation is often not called slavery, the conditions are the same. People are sold like objects, forced to work for little or no pay and are at the mercy of their "employers".

— Antislavery Society, What is Modern Slavery?

Forced labor in Sub-Saharan Africa is estimated at 660,000. This includes people involved in the illegal diamond mines of Sierra Leone and Liberia, which is also a direct result of the civil wars in these regions. In 2017, the International Labour Office estimated that 7 in every 1,000 people in Africa are victims of slavery.

Types of contemporary slavery

Hereditary slavery and corporate child labor in Africa

Sex trade

While institutional slavery has been banned worldwide, there are numerous reports of female sex slaves in areas without an effective government control, such as Sudan and Liberia, Sierra Leone, northern Uganda, Congo, Niger and Mauritania. In Ghana, Togo, and Benin, a form of (forced) religious prostitution known as trokosi ("ritual servitude") forcibly keeps thousands of girls and women in traditional shrines as "wives of the gods", where priests perform the sexual function in place of the gods.

Forced labour

Forced labor, which –strictly speaking– can be different from slavery, is defined as any work or services which people are forced to do against their will under the threat of some form of punishment. In the Democratic Republic of the Congo, the indigenous people are usually victims of their Bantu neighbors, who have replaced the positions once held by Arabs and Europeans.

We must work for the Bantu masters. We cannot refuse to do so because we are likely to be beaten or be victims of insults and threats. Even though we agree to work all day in the fields, we are still asked to work even more, for example, to fetch firewood or go hunting. Most of the time, they pay us in kind, a worn loincloth for 10 workdays. We cannot refuse because we do not have a choice.

— Antislavery Society, Interview with an indigenous man in the Congo

Child slave trade

The trading of children has been reported in modern Nigeria and Benin. The children are kidnapped or purchased for $20–70 each by slavers in poorer states, such as Benin and Togo, and sold into slavery in sex dens or as unpaid domestic servants for $350 each in wealthier oil-rich states, such as Nigeria and Gabon.

In April 2014, Boko Haram kidnapped 276 female students from Chibok, Borno. More than 50 of them soon escaped, but the remainder have not been released. Instead, the leader of Boko Haram, Abubakar Shekau, who has a reward of $7 million offered by the United States Department of State since June 2013 for information leading to his capture, announced his intention of selling them into slavery.

Ritual slavery

Ritual servitude (Trokosi) is a practice in Ghana, Togo, and Benin where traditional religious shrines take human beings, usually young virgin girls, in payment for services, or in religious atonement for alleged misdeeds of a family member—almost always a female. In Ghana and in Togo, it is practiced by the Ewe people in the Volta Region, and in Benin, it is practiced by the Fon.

Slavery by country

Chad

The practice of slavery in Chad, as in the Sahel states in general, is an entrenched phenomenon with a long history, going back to the trans-Saharan slave trade in the Sahelian kingdoms, and it continues today. As elsewhere in Central and West Africa, the situation reflects an ethnic, racial and religious rift. IRIN (Integrated Regional Information Networks) of the UN Office for the Coordination of Humanitarian Affairs reports children being sold to Arab herdsmen in Chad by their parents due to poverty.

Congo

Debt bondage-like slavery is rife in parts of Congo. According to the Global Slavery Index, approximately, over one million people are enslaved in the region of the Democratic Republic of Congo.

Ethiopia

Mahider Bitew, Children's Rights and Protection expert at the Ministry of Women's Affairs, says that some remote studies conducted in Dire Dawa, Shashemene, Awassa, and three other towns of the country indicate that the problem of child trafficking is very serious. According to a 2003 study, about one thousand children were trafficked via Dire Dawa to countries of the Middle East. The majority of those children were girls, most of whom were forced to be prostitutes after leaving the country. The International Labour Organization has identified prostitution as the worst form of child labor.

In Ethiopia, children are trafficked into prostitution, to provide cheap or unpaid labor, and to work as domestic servants or beggars. The ages of these children are usually between 10 and 18, and their trafficking is from the country to urban centers and from cities to the country. Boys are often expected to work in activities such as herding cattle in rural areas and in the weaving industry in Addis Ababa and other major towns. Girls are expected to take responsibilities for domestic chores, childcare, and looking after the sick, and to work as prostitutes.

Ghana, Togo, Benin

In parts of Ghana among the Ewe people, a family may be punished for an offense by having to turn over a virgin female to serve as a sex slave within the offended family. In this instance, the woman does not gain the title of "wife". In parts of Ghana, Togo, and Benin, shrine slavery persists, despite being illegal in Ghana since 1998. This system of slavery is sometimes called trokosi (in Ghana), or voodoosi in Togo and Benin, or ritual servitude. Young virgin girls are given as slaves in traditional shrines and are used sexually by the priests, in addition to providing free labor for the shrine.

Many Chinese prostitutes are trafficked to Ghana to service expatriate communities in the country, the Enslavement Protection Alliance-West Africa (EPAWA) investigations reveal. The Accra-based non-governmental organization told Citi Newsroom that victims are recruited under the guise of working as restaurant assistants. They are then confined and forced to provide sexual services.

Madagascar

Domestic servitude and forced labor are a continuing problem and increasing as a result of exacerbated poverty in Madagascar, according to a 2012 mission by the United Nations Special Rapporteur for contemporary forms of slavery. The UN Special Rapporteur identified children as particularly vulnerable and was particularly concerned about the enslavement of youth in mining and sexual exploitation or servile marriages.

Mali

Slavery continues to exist in Mali in all ethnic groups of the country but particularly among the Tuareg communities. The French formally abolished slavery in 1905, but many slaves remained with their masters until 1946 when large emancipation activism occurred. The first government of independent Mali tried to end slavery, but these efforts were undermined with the military dictatorship from 1968 until 1991. Slavery persists today with thousands of people still held in servitude; however, an active social movement called Temedt (which won the 2012 Anti-Slavery International award) has been pressuring the government for ending slavery in the country.

Although the Malian government denies that slavery continues, National Geographic writer Kira Salak claimed in 2002 that slavery was quite conspicuous and that she herself bought and then freed two slaves in Timbuktu. In addition, with the 2012 Tuareg Rebellion, there are reports of ex-slaves being recaptured by their former masters.

Mauritania

According to the Global Security Index Mauritania has one of the highest rates of vulnerability to slavery, ranking at number 4 in the region. A system exists now by which Arab Muslims—the bidanes—own black slaves, the haratines. An estimated 90,000 Mauritanians remain essentially enslaved. The ruling bidanes (the name means literally white-skinned people) are descendants of the Sanhaja Berbers and Beni Hassan Arab tribes who emigrated to northwest Africa and present-day Western Sahara and Mauritania during the Middle Ages. According to some estimates, up to 600,000 Mauritanians, or 20% of the population, are still enslaved, many of them used as bonded labour. Slavery in Mauritania was criminalized in August 2007. Malouma Messoud, a former Muslim slave has explained her enslavement to a religious leader:

"We didn't learn this history in school; we simply grew up within this social hierarchy and lived it. Slaves believe that if they do not obey their masters, they will not go to paradise. They are raised in a social and religious system that everyday reinforces this idea."

In Mauritania, despite slave ownership having been banned by law in 1981, hereditary slavery continues. Moreover, according to Amnesty International:

Not only has the government denied the existence of slavery and failed to respond to cases brought to its attention, it has hampered the activities of organizations which are working on the issue, including by refusing to grant them official recognition.

Imam El Hassan Ould Benyamin of Tayarat in 1997 expressed his views about earlier proclamations ending slavery in his country as follows:

[it] is contrary to the teachings of the fundamental text of Islamic law, the Quran ... [and] amounts to the expropriation from Muslims of their goods; goods that were acquired legally. The state, if it is Islamic, does not have the right to seize my house, my wife or my slave.

Biram Dah Abeid, often called the Mauritanian Nelson Mandela, "Le Spartacus Mauritanien", an anti-slavery activist and member of the Haratin ethnic group in Mauritania argues that

there is a kind of informal coalition – Beydanes [the slave owning caste], the state, police, judges, and imams – that prevents slaves from leaving their masters. "Whenever a slave breaks free while IRA [his antislavery group] is not aware and not present, police officers and judges help Arab-Berbers to intimidate the slave until he returns in submission".

Biram, along with 16 other activists, since 11 November 2014, is awaiting trial in Mauritania on multiple charges which include "violating public order" and "offending the authorities".

The story of Biram Dah Abeid, a prominent anti-slavery activist on trial, illustrates the troubled history and continued prevalence of slavery in Mauritania. Yet, Mauritanian human rights campaigners remain hopeful and believe that the trial will ultimately lead to positive long-term changes.

Niger

Niger continues to have significant problems with three forms of contemporary slavery: hereditary slavery, what Anti-Slavery International terms "passive slavery", and servile marriages called wahaya. Because of the continued problem of slavery and pressure from the Timidria organization, Niger became the first country in Western Africa to pass a law specifically criminalizing slavery. Despite the law, slavery persists throughout the different ethnic groups of the country, women are particularly vulnerable, and a 2002 census confirmed the existence of 43,000 slaves and estimated that the total population could be over 870,000 people. In a landmark case in 2008, the Economic Community of West African States (ECOWAS) Community Court of Justice found the government of Niger responsible for continuing a woman's slave status as part of a wahaya marriage and awarded her US$21,500.

Sudan

Sudan has seen a resurgence of slavery since 1983, associated with the Second Sudanese Civil War. Estimates of abductions range from 14,000 to 200,000 people.

In Sudan, animist and Christian captives in the civil war are often enslaved, and female prisoners are often used sexually, with their Muslim captors claiming that Islamic law grants them permission. According to CBS News, slaves have been sold for $50 per person. In 2001, CNN reported that the Bush administration was under pressure from Congress, including conservative Christians concerned about religious oppression and slavery, to address issues involved in the Sudanese conflict. CNN has also quoted the U.S. State Department's allegations: "The [Sudanese] government's support of slavery and its continued military action which has resulted in numerous deaths are due in part to the victims' religious beliefs."

Jok Madut Jok, professor of History at Loyola Marymount University, states that the abduction of women and children of the south by north is slavery by any definition. The government of Sudan insists that the whole matter is no more than the traditional tribal feuding over resources.

South Africa

Despite significant efforts made by the South African Government to combat trafficking in persons, the country has been placed on the "Tier 2 Watch List" by the U.S. Department of Trafficking in Persons for the past four years. South Africa shares borders with Namibia, Botswana, Zimbabwe, Lesotho, Mozambique and Eswatini. It has 72 official ports of entry "and a number of unofficial ports of entry where people come in and out without being detected" along its 5 000 km-long land borderline. The problem of porous borders is compounded by the lack of adequately trained employees, resulting in few police officials controlling large portions of the country's coastline.

Saturday, May 27, 2023

Astrophysical maser

From Wikipedia, the free encyclopedia
 
Aurorae on the north pole of Jupiter generate cyclotron masers (Hubble)

An astrophysical maser is a naturally occurring source of stimulated spectral line emission, typically in the microwave portion of the electromagnetic spectrum. This emission may arise in molecular clouds, comets, planetary atmospheres, stellar atmospheres, or various other conditions in interstellar space.

Background

Discrete transition energy

Like a laser, the emission from a maser is stimulated (or seeded) and monochromatic, having the frequency corresponding to the energy difference between two quantum-mechanical energy levels of the species in the gain medium which have been pumped into a non-thermal population distribution. However, naturally occurring masers lack the resonant cavity engineered for terrestrial laboratory masers. The emission from an astrophysical maser is due to a single pass through the gain medium and therefore generally lacks the spatial coherence and mode purity expected from a laboratory maser.

Nomenclature

Due to the differences between engineered and naturally occurring masers, it is often stated that astrophysical masers are not "true" masers because they lack oscillation cavities. However, the distinction between oscillator-based lasers and single-pass lasers was intentionally disregarded by the laser community in the early years of the technology.

This fundamental incongruency in language has resulted in the use of other paradoxical definitions in the field. For example, if the gain medium of a (misaligned) laser is emission-seeded but non-oscillating radiation, it is said to emit amplified spontaneous emission or ASE. This ASE is regarded as unwanted or parasitic (some researchers would add to this definition the presence of insufficient feedback or unmet lasing threshold): that is, the users wish the system to behave as a laser. The emission from astrophysical masers is, in fact, ASE but is sometimes termed superradiant emission to differentiate it from the laboratory phenomenon. This simply adds to the confusion, since both sources are superradiant. In some laboratory lasers, such as a single pass through a regeneratively amplified Ti:Sapph stage, the physics is directly analogous to an amplified ray in an astrophysical maser.

Furthermore, the practical limits of the use of the m to stand for microwave in maser are variously employed. For example, when lasers were initially developed in the visible portion of the spectrum, they were called optical masers. Charles Townes advocated that the m stand for molecule, since energy states of molecules generally provide the masing transition. Along these lines, some use the term laser to describe any system that exploits an electronic transition and the term maser to describe a system that exploits a rotational or vibrational transition, regardless of the output frequency. Some astrophysicists use the term iraser to describe a maser emitting at a wavelength of a few micrometres, even though the optics community terms similar sources lasers. The term taser has been used to describe laboratory masers in the terahertz regime, although astronomers might call these sub-millimeter masers and laboratory physicists generally call these gas lasers or specifically alcohol lasers in reference to the gain species. The electrical engineering community typically limits the use of the word microwave to frequencies between roughly 1 GHz and 300 GHz; that is, wavelengths between 30 cm and 1 mm, respectively.

Astrophysical conditions

The simple existence of a pumped population inversion is not sufficient for the observation of a maser. For example, there must be velocity coherence (light) along the line of sight so that Doppler shifting does not prevent inverted states in different parts of the gain medium from radiatively coupling. While polarisation in laboratory lasers and masers may be achieved by selectively oscillating the desired modes, polarisation in natural masers will arise only in the presence of a polarisation-state–dependent pump or of a magnetic field in the gain medium. Finally, the radiation from astrophysical masers can be quite weak and may escape detection due to the limited sensitivity (and relative remoteness) of astronomical observatories and due to the sometimes overwhelming spectral absorption from unpumped molecules of the maser species in the surrounding space. This latter obstacle may be partially surmounted through the judicious use of the spatial filtering inherent in interferometric techniques, especially very long baseline interferometry (VLBI).

The study of masers provides valuable information on the conditions—temperature, density, magnetic field, and velocity—in environments of stellar birth and death and the centres of galaxies containing black holes, leading to refinements in existing theoretical models.

Discovery

Historical background

In 1965 an unexpected discovery was made by Weaver et al.: emission lines in space, of unknown origin, at a frequency of 1665 MHz. At this time many researchers still thought that molecules could not exist in space, even though they had been discovered by McKellar in the 1940s, and so the emission was at first attributed to an unknown form of interstellar matter named Mysterium; but the emission was soon identified as line emission from hydroxide molecules in compact sources within molecular clouds. More discoveries followed, with water emission in 1969, methanol emission in 1970, and silicon monoxide emission in 1974, all emanating from within molecular clouds. These were termed masers, as from their narrow line widths and high effective temperatures it became clear that these sources were amplifying microwave radiation.

Masers were then discovered around highly evolved late-type stars (named OH/IR stars). First was hydroxide emission in 1968, then water emission in 1969 and silicon monoxide emission in 1974. Masers were also discovered in external galaxies in 1973, and in the Solar System in comet halos.

Another unexpected discovery was made in 1982 with the discovery of emission from an extra-galactic source with an unrivalled luminosity about 106 times larger than any previous source. This was termed a megamaser because of its great luminosity; many more megamasers have since been discovered.

A weak disk maser was discovered in 1995 emanating from the star MWC 349A, using NASA's Kuiper Airborne Observatory.

Evidence for an anti-pumped (dasar) sub-thermal population in the 4830 MHz transition of formaldehyde (H2CO) was observed in 1969 by Palmer et al.

Detection

The connections of maser activity with far infrared (FIR) emission has been used to conduct searches of the sky with optical telescopes (because optical telescopes are easier to use for searches of this kind), and likely objects are then checked in the radio spectrum. Particularly targeted are molecular clouds, OH-IR stars, and FIR active galaxies.

Known interstellar species

The following species have been observed in stimulated emission from astronomical environments:

Characteristics of maser radiation

The amplification or gain of radiation passing through a maser cloud is exponential. This has consequences for the radiation it produces:

Beaming

Small path differences across the irregularly shaped maser cloud become greatly distorted by exponential gain. Part of the cloud that has a slightly longer path length than the rest will appear much brighter (as it is the exponent of the path length that is relevant), and so maser spots are typically much smaller than their parent clouds. The majority of the radiation will emerge along this line of greatest path length in a "beam"; this is termed beaming.

Rapid variability

As the gain of a maser depends exponentially on the population inversion and the velocity-coherent path length, any variation of either will itself result in exponential change of the maser output.

Line narrowing

Exponential gain also amplifies the centre of the line shape (Gaussian or Lorentzian, etc.) more than the edges or wings. This results in an emission line shape that is much taller but not much wider. This makes the line appear narrower relative to the unamplified line.

Saturation

The exponential growth in intensity of radiation passing through a maser cloud continues as long as pumping processes can maintain the population inversion against the growing losses by stimulated emission. While this is so the maser is said to be unsaturated. However, after a point, the population inversion cannot be maintained any longer and the maser becomes saturated. In a saturated maser, amplification of radiation depends linearly on the size of population inversion and the path length. Saturation of one transition in a maser can affect the degree of inversion in other transitions in the same maser, an effect known as competitive gain.

High brightness

The brightness temperature of a maser is the temperature a black body would have if producing the same emission brightness at the wavelength of the maser. That is, if an object had a temperature of about 109K it would produce as much 1665-MHz radiation as a strong interstellar OH maser. Of course, at 109K the OH molecule would dissociate (kT is greater than the bond energy), so the brightness temperature is not indicative of the kinetic temperature of the maser gas but is nevertheless useful in describing maser emission. Masers have incredible effective temperatures, many around 109K, but some of up to 1012K and even 1014K.

Polarisation

An important aspect of maser study is polarisation of the emission. Astronomical masers are often very highly polarised, sometimes 100% (in the case of some OH masers) in a circular fashion, and to a lesser degree in a linear fashion. This polarisation is due to some combination of the Zeeman effect, magnetic beaming of the maser radiation, and anisotropic pumping which favours certain magnetic-state transitions.

Many of the characteristics of megamaser emission are different.

Maser environments

Comets

Comets are small bodies (5 to 15 km diameter) of frozen volatiles (e.g., water, carbon dioxide, ammonia, and methane) embedded in a crusty silicate filler that orbit the Sun in eccentric orbits. As they approach the Sun, the volatiles vaporise to form a halo and later a tail around the nucleus. Once vaporised, these molecules can form inversions and mase.

The impact of comet Shoemaker-Levy 9 with Jupiter in 1994 resulted in maser emissions in the 22 GHz region from the water molecule. Despite the apparent rarity of these events, observation of the intense maser emission has been suggested as a detection scheme for extrasolar planets.

Ultraviolet light from the Sun breaks down some water molecules to form hydroxides that can mase. In 1997, 1667-MHz maser emission characteristic of hydroxide was observed from comet Hale-Bopp.

Planetary atmospheres

It is predicted that masers exist in the atmospheres of gas giant planets. Such masers would be highly variable due to planetary rotation (10-hour period for Jovian planets). Cyclotron masers have been detected at the north pole of Jupiter.

Planetary systems

In 2009, S. V. Pogrebenko et al. reported the detection of water masers in the plumes of water associated with the Saturnian moons Hyperion, Titan, Enceladus, and Atlas.

Stellar atmospheres

Pulsations of the Mira variable S Orionis, showing dust production and masers (ESO)

The conditions in the atmospheres of late-type stars support the pumping of different maser species at different distances from the star. Due to instabilities within the nuclear burning sections of the star, the star experiences periods of increased energy release. These pulses produce a shockwave that forces the atmosphere outward. Hydroxyl masers occur at a distance of about 1,000 to 10,000 astronomical units (AU), water masers at a distance of about 100 to 400 AU, and silicon monoxide masers at a distance of about 5 to 10 AU. Both radiative and collisional pumping resulting from the shockwave have been suggested as the pumping mechanism for the silicon monoxide masers. These masers diminish for larger radii as the gaseous silicon monoxide condenses into dust, depleting the available maser molecules. For the water masers, the inner and outer radii limits roughly correspond to the density limits for maser operation. At the inner boundary, the collisions between molecules are enough to remove a population inversion. At the outer boundary, the density and optical depth is low enough that the gain of the maser is diminished. Additionally, the hydroxyl masers are supported chemical pumping. At the distances where these masers are found water molecules are disassociated by UV radiation.

Star-forming regions

Young stellar objects and (ultra)compact H II regions embedded in molecular clouds and giant molecular clouds, support the bulk of astrophysical masers. Various pumping schemes – both radiative and collisional and combinations thereof – result in the maser emission of multiple transitions of many species. For example, the OH molecule has been observed to mase at 1612, 1665, 1667, 1720, 4660, 4750, 4765, 6031, 6035, and 13441 MHz. Water and methanol masers are also typical of these environments. Relatively rare masers such as ammonia and formaldehyde may also be found in star-forming regions.

Supernova remnants

WISE image of IC 443, a supernova remnant with maser emission

The 1720 MHz maser transition of hydroxide is known to be associated with supernova remnants that interact with molecular clouds.

Extragalactic sources

While some of the masers in star forming regions can achieve luminosities sufficient for detection from external galaxies (such as the nearby Magellanic Clouds), masers observed from distant galaxies generally arise in wholly different conditions. Some galaxies possess central black holes into which a disk of molecular material (about 0.5 parsec in size) is falling. Excitations of these molecules in the disk or in a jet can result in megamasers with large luminosities. Hydroxyl, water, and formaldehyde masers are known to exist in these conditions.

Ongoing research

Astronomical masers remain an active field of research in radio astronomy and laboratory astrophysics due, in part, to the fact that they are valuable diagnostic tools for astrophysical environments which may otherwise elude rigorous quantitative study and because they may facilitate the study of conditions which are inaccessible in terrestrial laboratories.

Variability

Maser variability is generally understood to mean the change in apparent brightness to the observer. Intensity variations can occur on timescales from days to years indicating limits on maser size and excitation scheme. However, masers change in various ways over various timescales.

Distance determinations

Masers in star-forming regions are known to move across the sky along with the material that is flowing out from the forming star(s). Also, since the emission is a narrow spectral line, line-of-sight velocity can be determined from the Doppler shift variation of the observed frequency of the maser, permitting a three-dimensional mapping of the dynamics of the maser environment. Perhaps the most spectacular success of this technique is the dynamical determination of the distance to the galaxy NGC 4258 from the analysis of the motion of the masers in the black-hole disk. Also, water masers have been used to estimate the distance and proper motion of galaxies in the Local Group, including that of the Triangulum Galaxy.

VLBI observations of maser sources in late type stars and star forming regions provide determinations of their trigonometric parallax and therefore their distance. This method is much more accurate than other distance determinations, and gives us information about the galactic distance scale (e.g. the distance of spiral arms).

Open issues

Unlike terrestrial lasers and masers for which the excitation mechanism is known and engineered, the reverse is true for astrophysical masers. In general, astrophysical masers are discovered empirically then studied further in order to develop plausible suggestions about possible pumping schemes. Quantification of the transverse size, spatial and temporal variations, and polarisation state (typically requiring VLBI telemetry) are all useful in the development of a pump theory. Galactic formaldehyde masing is one such example that remains problematic.

On the other hand, some masers have been predicted to occur theoretically but have yet to be observed in nature. For example, the magnetic dipole transitions of the OH molecule near 53 MHz are expected to occur but have yet to be observed.

Inequality (mathematics)

From Wikipedia, the free encyclopedia https://en.wikipedia.org/wiki/Inequality...