Black Holes Light

Black Holes Light UpAstronomers Spot Black Holes Using NASA's Chandra X-Ray Observatory
September 1, 2006 — Not even light can escape a black hole's grip, but gas falling into a black hole can heat up and become an intense source of X-rays, at temperatures up to 1,000 times hotter than the sun. Astronomers use the Chandra X-Ray Observatory -- a NASA satellite -- to map these X-ray sources and study their properties

ANN ARBOR, Mich. -- They are deep and dense, and not even light can escape their grip. We're talking about black holes, but they may not be as dark as you think.
"If you have binoculars, you might be able to make out a smudge, which would be the nearest galaxies," says Jon Miller, an assistant professor of astronomy at the University of Michigan in Ann Arbor.
But what you won't see -- even with a telescope -- black holes! In fact, Miller doesn't even use one to study black holes. He uses his computer.

"I think it's really for the best that NASA doesn't let people like me drive billion-dollar satellites. So instead, we get data distributed through the computer networks," Miller tells DBIS.
These data reveal just how complex black holes are. As gravity pulls matter into the hole, it is heated 1,000-times hotter than the sun and forms mega-heated gases. As the hole's magnetic field pulls these gases into its center, it creates a light show.

Miller says, "Just before matter falls into the black hole, it can glow very brightly in X-rays." The Chandra X-ray Observatory takes X-ray photographs of these holes all over the universe.
According to Miller, every galaxy probably harbors a super massive black hole at the center of that galaxy. "I mean something that's a million or even billions of times the mass of our sun," he says. He hopes his research will help to prove not only what happens after black holes are formed, but also how they grow.

BACKGROUND: A team of astronomers led by the University of Michigan may know how black holes are lighting up the universe. New data from NASA's Chandra X-ray Observatory show for the first time that powerful magnetic fields are the key to these brilliant and startling light shows. By gaining deeper understanding of how black holes gather matter into themselves, astronomers also hope to learn more about other properties of black holes, including how they grow.

LIGHT FROM DARK: Black holes are the darkest objects in the universe. If a gas in a disk around a black hole loses energy, it will swirl toward the black hole, generating light along the way. In 1973, physicists suggested that magnetic fields could drive the generation of light by black holes. They would do this by generating friction in the gas and driving a wind from the disk that carries momentum outward. It is estimated that up to half of the total radiation in the universe since the Big Bang comes from material falling towards super-massive black holes.

WHAT CHANDRA FOUND: Chandra measures the amount of X-rays emitted at different energies, called X-ray spectroscopy. Spectroscopy is the study of light's "fingerprint," according to its color, which indicates its energy. Chemical elements each shine brightly at certain energies, so scientists can determine the chemical composition of an object. Chandra studied the X-ray spectra coming from a black hole system known as J1655 located in the Milky Way galaxy. The black hole was pulling material from a companion star into a disk, emitting the telltale radiation. The Michigan astronomers showed that the speed and density of the wind from the disk in J1655 corresponded to computer simulation predictions for winds driven by magnetic fields.
ABOUT BLACK HOLES: A black hole forms when a massive star has used up all its fuel. The reason the Sun and other stars emit light is because trillions of nuclear reactions are taking place at the cores. With core temperatures of millions of degrees, hydrogen atoms can convert into helium atoms, emitting radiation in the process. At some point, however, all the atoms are used up and no more nuclear fusion can take place. Without that outward counter-force to the pull of gravity, a star collapses inward, eventually reaching a point where the attractive gravitational force is so strong, not even light can escape. No one has ever observed the center of a black hole; until quite recently, such objects only existed in theory. But scientists surmise that a black hole has at its center an infinite density and an infinite gravitational field, as well as infinite entropy, which means no further change can take place. This is known as a "singularity." The event horizon of a black hole is not so much a physical surface as the theoretical point of no return for any object that gets caught in the black hole's powerful gravitational field.

The American Astronomical Society contributed to the information contained in the TV portion of this report.

New Method Developed To Weigh, Resolve Distant Black Holes

ScienceDaily (June 5, 2008) — Research presented to the American Astronomical Society meeting in St. Louis June 2 offers astronomers a new, simple method to learn about black holes up to eight billion light years away – thousands of times farther away than black holes can be measured today.

Dr. Marc Seigar, assistant professor of physics and astronomy in the College of Science and Math at the University of Arkansas at Little Rock, and his research team have concluded that the larger the black hole at the center of a spiral galaxy, the tighter the galaxy’s arms wrap around itself. If correct, the simple relationship would give researchers an easy way to learn about black holes.

“This is a really easy way to determine the masses of these super-massive black holes at the centers of galaxies that are very far away,” Seigar said. “This gives us a way to measure the size of these far away black holes.”

Since super-massive black holes were discovered in nearby galaxies, researchers have been determining their masses by looking at how fast the stars were moving in the very central regions of those galaxies. But that method only works for relatively nearby galaxies, Seigar said.
“For more distant galaxies out to the distances we’re talking about, you have to develop alternative methods,” Seigar said. “And we have developed such a method.”

The method he described to the Astronomical Society involves taking a snapshot of a distant galaxy and measuring how tightly the spiral arms wrap around the galaxy, or the wrapping angle. He determined that the more massive the black hole, the tighter the spiral arms wrap around the galaxy, which indicates a small wrapping angle.

Seigar’s team studied photographs of 27 spiral galaxies, including our galaxy, the Milky Way, and its nearest neighbor, the Andromeda Galaxy. Galaxies with the smallest black holes had spiral arms with wrapping angles of up to 43 degrees. Those with biggest black holes had spiral arms at angles of only seven degrees between their central bulges.

“One of the important reasons to learn about the every distant black holes is, when you are looking at galaxies very far away, you are looking at them as they were in the past, so you can learn about how masses of black holes grow over time, ” Seigar said.

The black holes he is studying are super-massive black holes that are millions or billions times more massive than our sun. Since they seem to be found at the centers of all galaxies, they could be a key element of how galaxies form in the first place.

His studies also indicate that the mass of a black hole may depend on how centrally concentrated the dark matter is in a galaxy. “But that is a hypothesis that has yet to be proven,” he said. “We’re going to work on that.”

Seigar joined UALR’s faculty in 2007 following a stint as an assistant project scientist and McCue Fellow at the University of California-Irvine. His other experience includes postdoctoral research associate at the University of California-Irvine, adjunct professor at the University of Hawaii-Hilo, postdoctoral research associate at the University of London’s Imperial College and at Ghent University in Belgium. He also was a visiting astronomer at the Space Telescope Science Institute.

Seigar, who earned a Ph.D. in astrophysics at John Moores University in Liverpool, teaches Introduction to Astronomy at UALR as well as performing research in the structure, dynamics and star formation in spiral galaxies, and the nature of intracluster light in clusters of galaxies.
“Since my thesis I have been interested in the overall structure, morphology and dynamics of nearby galaxies, especially disk galaxies,” Seigar said.

He is involved in the Carnegie-Irvine Nearby Galaxies Survey (CINGS), a comprehensive optical and infrared imaging survey of the 600 brightest galaxies in the southern-hemisphere sky, being carried out at the 2.5-meter Du Pont telescope at Las Campanas Observatory. He is also involved in the Arkansas Galaxy Evolution Survey (AGES), part of which is to conduct a census of super-massive black holes in the universe.

ScienceDaily (Dec. 28, 2006) — Research by UK astronomers, published in Nature (7th December 2006) reveals that the processes at work in black holes of all sizes are the same and that supermassive black holes are simply scaled up versions of small Galactic black holes

For many years astronomers have been trying to understand the similarities between stellar-mass sized Galactic black hole systems and the supermassive black holes in active galactic nuclei (AGN).In particular, do they vary fundamentally in the same way, but perhaps with any characteristic timescales being scaled up in proportion to the mass of the black hole. If so, the researchers proposed, we could determine how AGN should behave on cosmological timescales by studying the brighter and much faster galactic systems.

Professor Ian McHardy, from the University of Southampton, heads up the research team whose findings are published today (along with colleagues Drs Elmar Koerding and Christian Knigge and Professor Rob Fender, and Dr Phil Uttley, currently working at the University of Amsterdam). Their observations were made using data from NASA's Rossi X-ray Timing Explorer and XMM Newton's X-ray Observatory.

Professor McHardy comments, "By studying the way in which the X-ray emission from black hole systems varies, we found that the accretion or 'feeding' process - where the black hole is pulling in material from its surroundings - is the same in black holes of all sizes and that AGN are just scaled-up Galactic black holes. We also found that the way in which the X-ray emission varies is strongly correlated with the width of optical emission lines from black hole systems."
He adds, "These observations have important implications for our understanding of the different types of AGN, as classified by the width of their emission lines. Thus narrow line Seyfert galaxies, which are often discussed as being unusual, are no different to other AGN; they just have a smaller ratio of mass to accretion rate."

The research shows that the characteristic timescale changes linearly with black hole mass, but inversely with the accretion rate (when measured relative to the maximum possible accretion rate). This result means that the accretion process is the same in black holes of all sizes. By measuring the characteristic timescale and the accretion rate, the team argues this simple relationship can help determine black hole masses where other methods are very difficult, for example in obscured AGN or in the much sought after intermediate mass black holes.
Professor McHardy continues: "Accretion of matter into a black hole produces strong X-ray emission from very close to the black hole itself. So, studying the way in which the X-ray emission varies with time, known as the X-ray lightcurves, provides one of the best ways of understanding the behaviour of black holes.

It has been known for over two decades that characteristic timescales can be seen in the X-ray lightcurves of Galactic black hole systems. The timescales are short (second) and so can be found in short observations. However to find the equivalent timescales in AGN is much harder as we must observe for months or years."