Journey to the Center of the Milky Way

"The black hole came into existence billions of years ago, perhaps as very massive stars collapsed at the end of their life cycles and coalesced into a single, supermassive object."

-Andrea Ghez, professor of physics and astronomy, UCLA

For years, astronomers speculated that a giant, mysterious force lay at the center of the Milky Way 26,000 light years or 158 trillion miles away, but it wasn't until four years ago that definitively showed what it was.

(The image above of our Milky Way galaxy's core reveals a star-forming region as recorded at several wavelengths invisible to the eye. Red indicates radio-wave emission, green indicates radiation in the mid-infrared, and blue is X-ray emission. The arrow indicates the super massive black hole at our galaxy's center with a mass of about 2.6 million times the mass of our sun. Q. Daniel Wang, U. Mass).

Ghez's research focuses on the origin and early life of stars and planets, and the distribution and nature of the matter at the center of our galaxy. Using new techniques for peering into the dusty heart of the galaxy, Ghez's observations proved that scores of stars were rapidly orbiting what could only be a black hole. But it wasn't the kind of garden-variety black hole created when a star explodes and dies; it was hundreds of thousands of times as powerful -- a "supermassive" black hole- at the center of our galaxy.

Black holes are collapsed stars so dense that nothing can escape their gravitational pull, not even light. Black holes cannot be seen directly, but their influence on nearby stars is visible, and provides a signature, Ghez said. The supermassive black hole, with a mass more than 3 million times that of our sun, is in the constellation of Sagittarius. Our galaxy's core Black Hole is called Sagittarius A*, or Sgr A*, located due south in the summer sky.

What's inside a black hole is one of the biggest mysteries in physics. Einstein's general-relativity theory that predicted black holes in the first place says that all the matter inside them gets squashed into a central point of infinite density called a singularity. But then, "things break down mathematically", says Christian Böhmer of University College London, in the UK. When matter gets swallowed by a black hole, according to a radical new theory proposed by Bohmer called quantum loop, it could fall into another universe contained inside the black hole, or get trapped inside a wormhole-like connection to a second black hole.

Since 1995 Ghez has been using the W.M. Keck Observatory's 10-meter Keck I Telescope atop Mauna Kea in Hawaii - the world's largest optical and infrared telescope- to study the movement of 200 stars close to the galactic center. She has made measurements using a technique she refined, called infrared speckle interferometry, and for the last few years, an even more sophisticated technique, called adaptive optics, a new laser virtual star, which enables her to see more of the densely packed stars in this region.

Twenty stars near the galactic center are orbiting ever closer to the black hole at a blinding speed of up to 3 million miles per hour about 10 times the speed at which stars typically move.

Her discoveries, along with the work of scientists studying other galaxies, have led astronomers to the surprising conclusion that most, if not all, of the universe's hundreds of billions of galaxies have supermassive black holes at their core. Even more striking, the astronomers have found that the black holes' mass and nature are closely related to the size and makeup of the surrounding galaxies.

Ghez earned her Ph.D. from the California Institute of Technology and her B.S. from the Massachusetts Institute of Technology; she was a Hubble Postdoctoral Research Fellow at the University of Arizona's Steward Observatory. She joined UCLAs faculty in 1994.

Black holes appear to be both creators and destroyers -- swallowing stars or gases that come too close while also spewing out jets of super-high-energy particles and radiation generated by this violent feeding process. The jets, which can be millions of light-years in length, are believed to seed galaxies with the mass and energy that will, in time, become new stars and perhaps even planets.

Ghez and UCLA colleague Mark Morris, a professor of physics and astronomy, reported the detection of remarkably stormy conditions in a hot plasma being pulled into Sagittarius A*. This detection of the hot plasma is the first in an infrared wavelength, where most of the disturbed plasmas energy is emitted, and was made using the Keck II Telescope.

Plasma is a hot, ionized, gas-like matter, a fourth state of matter- distinct from solids, liquids and gases believed to make up more than 99 percent of the visible universe, including the stars, galaxies and the vast majority of the solar system.

The supermassives are drawing astronomers and astrophysicists back into black hole research. In 1915, based on purely theoretical calculations, Albert Einstein laid the groundwork for the existence of these bizarre phenomena, which have such strong gravitational pull that not even light can escape them. But research on them languished for decades because there was no way to observe them directly.

The Hubble Space Telescope provided the first real evidence of the existence of supermassives-- revealing in 1994 that something was orbiting rapidly around the nuclei of some distant galaxies, suggesting the presence of a huge mass contained in a very small area.

Since then, the Hubble, NASA's orbiting Chandra X-Ray Observatory, the Keck and other very large, high-resolution ground telescopes have begun to unravel more about these central black holes.

Mysteries abound. Many researchers have offered theories of how supermassive black holes might have formed, but there is no consensus. Were they created in the early universe when exploding stars were larger, or are they created by the merger of galaxies with smaller black holes at their center?

There is also the puzzling question of why some are active -- feeding regularly on stars around them -- while others are nearly dormant. Ghez added to the mystery recently by reporting that some of the stars orbiting the Milky Way's central black hole are quite young, even though the galaxy is mature and its nucleus has long been dormant.

But dormancy can be temporary, as Suvi Gezari of the California Institute of Technology documented recently. Using the telescope on NASA's orbiting Galaxy Evolution Explorer -- which measures ultraviolet light from the early universe -- her team detected a distinctive flare from a distant galaxy and watched it diminish over time. They concluded that they had seen an unfortunate star stray too close to its galaxy's central black hole, where the star was torn apart and then swallowed by the force of its gravity. The bright flare -- a rarely witnessed event -- was the result of this "feeding."

"Most of these are sleeping cosmic beasts, just sitting there," Gezari said. "So we have to scan the skies to see those very rare times that there's a burst of radiation as the black hole feeds."

The fast pace of the recent discoveries is largely the result of the newer orbiting observatories and extremely powerful ground telescopes that have begun operating in the past decade. NASA's "Beyond Einstein" initiative was approved by Congress several years ago to speed development of space-based observatories and probes designed to tell us more about the early universe and the forces that ruled it.

But tight agency budgets have slowed the initiative, and most of the Beyond Einstein probes won't be launched for years, if at all. The proposed orbiting X-ray observatory Constellation-X would be especially valuable in learning more about the structure and dynamics of supermassive black holes -- measuring, for instance, the powerful spin of the accretion disk -- but that project has been put on hold.

Posted by Casey Kazan.

Comments

The speed of the orbiting disc would be fascinating to know. Bu again, at what speed would matter falling into the black hole pass through the event horizon? Under the force of gravity, it would speed up, but to what? and how long would the decent take once commenced. What effect could this super gravity have on time? Not the space-time continuum.

Posted by: Barrie O'Leary | January 13, 2009 at 05:25 AM

Mr. Hawking is still quite an expert in black holes.

Agree with 'sagittarius A' It was alreday known quite some time agò.
Nice to look at it with new interferometers and more modern multispectral instruments.

If it keeps united an entire galaxy with a number of stars ranging from 200 to 400 billions then it must be supermassive.

What it creates inside is and will remain one of the upmost mistery of this universe....
Difficult to explore inside.....difficult ...to measure...difficult...

Quantum generated parallel universe from the strage matter it keeps inside ??
Pipes (worm holes)to parallel universes ??
Possible.

To talk 'space-time web' in a black hole of such mass it is unusual......Singularities or mini-singularities.....inferred to exist at the center....

How long time to evapourate ?? LONG...Nobody really knows.

How it was formed ??

The theory of the initial gigastars...fully unstable and collapsed...at a joung universe is the best .
The Gigarstars exploded with 'quasar type of bangs'... Quasars explosions in turn collapsed into supermassive Black holes ??? Likely.
These have formed around star and planets...sucking everything nearby...they have formed an entire galaxy.

Andromeda (M31) in the local group seems to have 3 main black holes in the central zone ...Why ??
Do not know.

Black holes are powerfull and a bit scary things.

Regards

Very good article ...that I would rate at 4 points.

Posted by: claudio | January 13, 2009 at 12:14 PM

Someone correct me if I'm wrong; when a super-massive star dies it becomes a 'black hole'. BEFORE it became a 'black hole' it was a solid object; a STAR. So, would it not follow that, instead of a black 'hole', there would be a black SPHERE or BALL...WITH A GRAVITATIONAL PULL SO STRONG THAT NO FORM OF MASS OR ENERGY CAN ESCAPE IT IF CAUGHT???? SOMETHING existed there before, so something should still be there after that star dies. Things don't 'disappear' into it; they are just crushed down to inconsequential atoms and the only thing that CAN escape (it has been proven) are X-rays, and THEY escape from the poles.

People, PLEASE drop the Disney image of 'THE BLACK HOLE' (or the SCI-FI CHANNEL movie 'BLACK HOLE') and call it what it really is: A BLACK SPHERE!!

Posted by: Marty Ferguson | January 16, 2009 at 08:35 PM