NASA: Portrait of a Doomed Asteroid

A new study provides a possible explanation of mysterious X-ray flares detected by the Chandra K-ray Observatory for several years in the region of Sagittarius A*, or Sgr A*.

The study suggests a cloud around Sgr A*, a supermassive black hole at the center of our Milky Way Galaxy, which contains hundreds of trillions of asteroids and comets that have been stripped from their parent stars.

The flares occur when asteroids of six miles or larger in radius are consumed by the black hole.

An asteroid that undergoes a close encounter with another object, such as a star or planet, can be thrown into an orbit headed towards Sgr A*.

If the asteroid passes within about 100 million miles of the black hole, roughly the distance between the Earth and the sun, it is torn into pieces by the tidal forces from the black hole.

These fragments would then be vapourised by friction as they pass through the hot, thin gas flowing onto Sgr A*, similar to a meteor heating up and glowing as it falls through Earth's atmosphere.

A flare is produced and eventually the remains of the asteroid are swallowed by the black hole.

Image Credit: Illustrations: NASA/CXC/M.Weiss

NASA Chandra: Milky Way’s Black Hole Devouring Asteroids

Astronomers from U.S. space agency Nasa and the University of Leicester in the UK have discovered a giant black hole that is vapourising and devouring asteroids. This black hole is located at the centre of the Milky Way galaxy.

Astronomers have detected X-ray flares from Sagittarius A - a super massive black hole - at least once in a day.

The brightness of the flares keeps varying from time to time and the flares last a few hours. These were detected from NASA's Chandra X-ray Observatory.

Sagittarius A is surrounded by a huge thick cloud that contains trillions of asteroids and comets. Asteroids passing within a 100 million miles of the black hole - roughly the distance between the Earth and the sun - seem to be torn into pieces by the tidal forces from the black hole.

These fragments are then vaporized by friction as they pass through the hot, thin gas flowing onto Sagittarius A. The process is similar to a meteor heating up and glowing as it falls through the Earth's atmosphere. A flare is produced when it enters the black hole and the remains of the asteroid are swallowed eventually by the black hole.

According to the astronomers, a huge asteroid that is located near a black hole can generate the huge flares that can easily be observed through Chandra. However, the smaller asteroids could be difficult to spot because the flares they generate would be fainter.

Astronomers are also planning, sometime in the future, to learn more about the frequency and brightness of flares. The hope is that this work will help them understand the formation of asteroids and planets in the harsh environment of Sagittarius A.

"An asteroid's orbit can change if it ventures too close to a star or planet near Sagittarius A," said Sergei Nayakshin from the University of Leicester, "If it's thrown toward the black hole, it's doomed."

Tracking S-Stars Orbiting the Milky Way's Central Black Hole - YouTube video

In a 16-year long study, using several of ESO's flagship telescopes, a team of German astronomers has produced the most detailed view ever of the surroundings of the monster lurking at our Galaxy's heart — a supermassive black hole.

The research has unravelled the hidden secrets of this tumultuous region by mapping the orbits of almost 30 stars, a five-fold increase over previous studies. One of the stars has now completed a full orbit around the black hole.

By watching the motions of 28 stars orbiting the Milky Way's most central region with admirable patience and amazing precision, astronomers have been able to study the supermassive black hole lurking there. It is known as "Sagittarius A*" (pronounced "Sagittarius A star").

The new research marks the first time that the orbits of so many of these central stars have been calculated precisely and reveals information about the enigmatic formation of these stars — and about the black hole to which they are bound.

The interstellar dust that fills the Galaxy blocks our direct view of the Milky Way's central region in visible light. So astronomers used infrared wavelengths that can penetrate the dust to probe the region. While this is a technological challenge, it is well worth the effort. "The Galactic Centre harbours the closest supermassive black hole known. Hence, it is the best place to study black holes in detail," argues the study's first author, Stefan Gillessen.

The team used the central stars as "test particles" by watching how they move around Sagittarius A*. Just as leaves caught in a wintry gust reveal a complex web of air currents, so does tracking the central stars show the nexus of forces at work at the Galactic Centre.

These observations can then be used to infer important properties of the black hole itself, such as its mass and distance. The new study also showed that at least 95% of the mass sensed by the stars has to be in the black hole. There is thus little room left for other dark matter.

For the first time the number of known stellar orbits is now large enough to look for common properties among them. "The stars in the innermost region are in random orbits, like a swarm of bees," says Gillessen.

"However, further out, six of the 28 stars orbit the black hole in a disc. In this respect the new study has also confirmed explicitly earlier work in which the disc had been found, but only in a statistical sense. Ordered motion outside the central light-month, randomly oriented orbits inside that's how the dynamics of the young stars in the Galactic Centre are best described."

One particular star, known as S2, orbits the Milky Way's centre so fast that it completed one full revolution within the 16-year period of the study. Observing one complete orbit of S2 has been a crucial contribution to the high accuracy reached and to understanding this region.

Yet the mystery still remains as to how these young stars came to be in the orbits they are observed to be in today. They are much too young to have migrated far, but it seems even more improbable that they formed in their current orbits where the tidal forces of the black hole act. Excitingly, future observations are already being planned to test several theoretical models that try to solve this riddle.

"ESO still has much to look forward to," says Genzel. "For future studies in the immediate vicinity of the black hole, we need higher angular resolution than is presently possible." According to Frank Eisenhauer, principal investigator of the next generation instrument GRAVITY, ESO will soon be able to obtain that much needed resolution.

"The next major advance will be to combine the light from the four 8.2-metre VLT unit telescopes a technique known as interferometry. This will improve the accuracy of the observations by a factor 10 to 100 over what is currently possible.

This combination has the potential to directly test Einstein's general relativity in the presently unexplored region close to a black hole."

credit: ESO/ S. Gillessen, R. Genzel

source: www.eso.org

ESA ESO VLT: Newborn Massive Stars Dwarf Full-Grown Stellar Giants

Artist’s impression illustrating the formation process of massive stars. 

At the end of the formation process, the surrounding accretion disk disappears, revealing the surface of the young star. 

At this phase the young massive star is much larger than when it has reached a stable equilibrium.

CREDIT: Lucas Ellerbroek/Lex Kaper University of Amsterdam

Massive stars generally start out life much bigger than they will be in maturity, a new study seems to confirm.

Astronomers from the University of Amsterdam got a rare look at a massive star in the process of forming and found that the star will contract until it has reached a stable equilibrium.

The researchers studied the young star B275, which lies in the Omega Nebula, also called the Swan Nebula or Messier 17. This hotbed of gas, dust and young stars lies approximately 5,500 light-years from Earth, in the direction of the Sagittarius constellation.

Astronomers typically struggle to obtain clear observations of a massive star as it is forming, since newborn stars are deeply embedded and obscured in their parent clouds of gas and dust.

Peering through the haze
To lift the veil on the process of star formation, the researchers sifted through ultraviolet and infrared data collected from a powerful spectrograph instrument, called the X-shooter, on the European Space Agency's Very Large Telescope at the Paranal Observatory in Chile.

"The large-wavelength coverage of X-shooter provides the opportunity to determine many stellar properties at once, like the surface temperature, size, and the presence of a disk," study lead author Bram Ochsendorf said in a statement.

Ochsendorf analyzed the data as part of his master's research project at the University of Amsterdam.

The results indicate that B275 is about three times larger than stars that are about seven times more massive than our sun and have reached the so-called main sequence phase of their lives.

The main sequence phase represents a specific stage of stellar evolution in which a star burns hydrogen into helium. (Our own sun is currently in its main sequence.)

The team's findings appear to confirm a theory of star formation predicting that a newly formed massive star will contract until it reaches a more stable state.

Milky Way's Galactic Gobbling Leaves Star 'Crumbs'

Artist's concept of the four tails of the Sagittarius dwarf galaxy (orange clump on left of the image) orbiting the Milky Way.

The bright yellow circle to the right of the Milky Way's center is our sun (not to scale). We can see the Sagittarius galaxy's star tails stretching across the sky.

CREDIT: Amanda Smith, Institute of Astronomy, University of Cambridge

Our Milky Way galaxy is a messy eater, leaving streams of star "crumbs" spread across the sky after chomping its smaller neighbors, a new study reports.

Astronomers have found two such streams emanating from the Sagittarius dwarf galaxy, torn off by the Milky Way's huge gravitational pull.

The two newfound star tails are in the southern galactic hemisphere, and they meet up with two others previously known from Sagittarius in the northern galactic hemisphere.

"Sagittarius is like a beast with four tails," study co-author Wyn Evans, of the University of Cambridge in the United Kingdom, said in a statement.

NASA's Hubble Observes Young Dwarf Galaxies Bursting With Stars

This image reveals 18 tiny galaxies uncovered by NASA's Hubble Space Telescope. 

The puny galaxies, shown in the postage stamp-sized images, existed 9 billion years ago and are brimming with star birth. 

Hubble's Wide Field Camera 3 and Advanced Camera for Surveys spied the galaxies in a field called the Great Observatories Origins Deep Survey (GOODS). 

The galaxies are among 69 dwarf galaxies found in the GOODS (marked by green circles in the large image) and other fields.

Images of the individual galaxies were taken November 2010 to January 2011.
 

The large image was taken between Sept. 2002 and Dec. 2004, and between Sept. 2009 and Oct. 2009. 

(Credit: NASA, ESA, A. van der Wel (Max Planck Institute for Astronomy, Heidelberg, Germany), H. Ferguson and A. Koekemoer (STScI.), and the CANDELS team)

ESA Hubble: First Globular Cluster Outside the Milky Way

The object shown in this beautiful Hubble image, dubbed Messier 54, could be just another globular cluster, but this dense and faint group of stars was in fact the first globular cluster found that is outside our galaxy.

Discovered by the famous astronomer Charles Messier in 1778, Messier 54 belongs to a satellite of the Milky Way called the Sagittarius Dwarf Elliptical Galaxy.

Messier had no idea of the significance of his discovery at the time, and it wasn’t until over two centuries later, in 1994, that astronomers found Messier 54 to be part of the miniature galaxy and not our own.

Current estimates indicate that the Sagittarius dwarf, and hence the cluster, is situated almost 90 000 light-years away — more than three times as far from the centre of our galaxy than the Solar System.

Ironically, even though this globular cluster is now understood to lie outside the Milky Way, it will actually become part of it in the future.

The strong gravitational pull of our galaxy is slowly engulfing the Sagittarius dwarf, which will eventually merge with the Milky Way creating one much larger galaxy.

This picture is a composite created by combining images taken with the Wide Field Channel of Hubble’s Advanced Camera for Surveys.

Light that passed through a yellow-orange (F606W) was coloured blue and light passing through a near-infrared filter (F814W) was coloured red.

The total exposure times were 3460 s and 3560 s, respectively and the field of view is approximately 3.4 by 3.4 arcminutes.

Credit: ESA/Hubble & NASA

Sagittarius Dwarf elipitcal galaxy

A computer generated image released by the journal Nature shows the impact of the Sagittarius Dwarf elipitcal galaxy (blue stream of stars) with the Milky Way Galaxy (multicoloured disk), against a background of galaxies seen in the Hubble Deep Field.

A new theory posits that the formation of the arms of the Milky Way, a galaxy of some 200 billion stars with spiral limbs that whirl around a thin disk, was formed when it was hit by the dwarf galaxy, sending cascades of stars flying to the galactic rim.

The giant impact sent streams of stars from both galaxies. The stars were eventually tugged outward by the Milky Way's rotation into the limbs that we perceive today.

Picture: Nature/Erik Tollerud/AFP/Getty Images

ESA ESO VLT /VST Image: Omega Nebula or the Swan Nebula

This photo released by the European Southern Observatory shows the first released image of the star-breeding region in the constellation of Sagittarius known as the Omega Nebula or the Swan Nebula taken by a new telescope, the VLT Survey Telescope or VST.

It is the largest telescope of its kind in the world, able to capture in visible light a field of view that is twice as broad as the full Moon. The VST has been built on a mountain top in northern Chile's Atacama Desert, benefiting from viewing conditions in one of the driest and least light-polluted places on Earth.
 
Picture: AFP/ESO

The Milky Way

The centre of our Galaxy is a busy place. In visible light, much of the Galactic Center is obscured by opaque dust.

In infrared light, however, dust glows more and obscures less, allowing nearly one million stars to be recorded in the above image.

The Galactic Centre itself appears glowing on the lower left and is located about 30,000 light years away towards the constellation of Sagittarius.

The Galactic Plane of our Milky Way Galaxy, the plane in which the Sun orbits, is identifiable by the dark diagonal dust lane.

The absorbing dust grains are created in the atmospheres of cool red-giant stars and grow in molecular clouds.

The region directly surrounding the Galactic Centre glows brightly in radio and high-energy radiation. The Galactic Centre is thought to house a large black hole.

Large Megallenic Cloud - LMC

The Large Magellanic Cloud (LMC) is a nearby irregular galaxy, and is a satellite of the Milky Way.

It is visible as a faint "cloud" in the night sky of the southern hemisphere, straddling the border between the constellations of Dorado and Mensa.

At a distance of slightly less than 50 kiloparsecs (≈160,000 light-years), the LMC is the third closest galaxy to the Milky Way, with the Sagittarius Dwarf Spheroidal (~ 16 kiloparsecs) and Canis Major Dwarf Galaxy (~ 12.9 kiloparsecs) lying closer to the center of the Milky Way.

It has a mass equivalent to approximately 10 billion times the mass of our Sun (10¹⁰ solar masses), making it roughly 1/10 as massive as the Milky Way, and a diameter of about 14,000 light-years.

The LMC is the fourth largest galaxy in the Local Group, the first, second and third largest places being taken by Andromeda Galaxy (M31), our own Milky Way Galaxy, and the Triangulum Galaxy (M33), respectively.

While the LMC is often considered an irregular type galaxy (the NASA Extragalactic Database lists the Hubble sequence type as Irr/SB(s)m), the LMC contains a very prominent bar in its center, suggesting that it may have previously been a barred spiral galaxy.

The LMC's irregular appearance is possibly the result of tidal interactions with both the Milky Way, and the Small Magellanic Cloud (SMC).