Forces of Creation: Black Holes Spark Star Formation .....galaxy formation

pedro martori

2005-02-17 04:41:00 UTC

Matter Rides Black Hole's Space-Time Wave
By Robert Roy Britt
Senior Science Writer
posted: 10 January 2005
01:52 pm ET

SAN DIEGO -- Armed with cosmic speed guns and other high-tech devices, astronomers have witnessed amazing speeds around one black hole and an exotic wave in space-time careening around another.

The findings are among the most convincing ever of the incredible velocities and distortions that occur very close to black holes, and they help provide better estimates of the masses of the black holes. They also showcase a new method for getting an even better handle on these gravitational behemoths.

In one finding, a spinning black hole appears to create an orbiting wave. In a gross oversimplification, the process is similar to the wobble of a spinning top. The other study found evidence of hotspots -- perhaps blobs of hot gas the size of the Sun, or maybe regions lit by magnetic energy -- travelling at 10 percent the speed of light.

The results were presented here Monday at a meeting of the American Astronomical Society.

Black hole basics

Black holes are so dense they can trap light. They can't be seen, but astronomers find them by noting their gravitational effect on surrounding objects or by seeing X-rays and other radiation kicked up in their vicinity when gas is superheated as it swirls in at phenomenal speeds.

The infalling gas forms a thin disk, theory says. From this accretion disk come the X-rays used in the new research.

Any object with mass warps the space and time around it, in much the same way a heavy object deforms a stretched elastic sheet. Light passing by a very massive star or galaxy can be noticeably bent, for example.

Einstein's work predicts all this. But beyond Einstein, even stranger things are predicted. If an object spins, it further distorts space-time; imagine the elastic sheet being twisted by a heavy, spinning heavy.

The effect is called frame dragging. It is a modification to the simpler aspects of gravity set out by Newton. Working from Einstein's relativity theory, Austrian physicists Joseph Lense and Hans Thirring predicted frame dragging in 1918. (It is also known as the Lense-Thirring effect.)

Other studies have found evidence for spinning black holes and the warping of space-time around them. Even the rotation of Earth has been shown to distort nearby space-time, causing satellites to be dragged by 6 feet (2 meters) every year.

Frame dragging may play an important role in the twisted physics that cause black holes not just to swallow light and matter, but to spit out tremendous amounts of hot gas in high-velocity jets seen in several studies.

A merry-go-round

In observations by NASA's orbiting Rossi X-ray Timing Explorer, scientists examined the energy given off by iron gas. The light waves were stretched as the light struggled to climb out of the black hole's gravitational clutches.

The data revealed matter orbiting the relatively small black hole hundreds of times per second, "glowing like light bulbs on a merry-go-round," said Jeroen Homan of MIT.

The effect seen can be described by frame dragging, said co-researcher Jon Miller of the Harvard-Smithsonian Center for Astrophysics. Confident in the finding, he still remains cautious.

"It may be that other explanations turn out to be better, "Miller told SPACE.com. "It is not a shut case."

The results will be published in the Astrophysical Journal Letters.

Blobs of gas

The other study, using the European Space Agency's XMM-Newton satellite, found three apparent blobs of hot gas flying around a different black hole at 20,000 miles per second (32,190 kilometers per second). That's 10 percent of light-speed. The blobs are very close to the black hole and allow astronomers to calculate a more precise mass and size of the object.

The black hole, anchoring a galaxy known as Markarian 766, contains about 100 million times the mass of the Sun.

The black hole encompasses a region just smaller than the orbit of Mercury. The blobs of iron gas are at a distance equal to the orbit of Jupiter. But unlike Jupiter's 12-year orbit, the blobs circle the black hole in a mere 27 hours.

The speed was measured using the Doppler technique, same as a cop's radar gun. It's also the phenomenon that makes an ambulance siren change pitch when heading toward you (the waves are compressed) versus away from you (the waves are stretched).

It is the first time material has been observed making a complete orbit so close to a black hole, said study member Lance Miller of Oxford University.

Miller and his colleague, study leader Jane Turner of NASA and the University of Maryland Baltimore County, acknowledged that similar but tentative results were announced in September by a European group. And other studies have seen evidence for matter near a black hole, even possibly sliding beyond the point of no return.

In an interview, Turner said the new results were "more clear" and "easy to interpret" compared to previous observations.

Both studies presented today are "pioneering results" that point the direction for future observations that could better pin down the physics of black holes, said Fred Lamb, a University of Illinois researcher who was not involved in the research.

a.. Animation of the Space-Time Wave
b.. The Problem With Gravity: Numbers that Don't Add Up
c.. The True Shape of Black Holes
d.. Earth Warps Space-Time, Too

Forces of Creation: Black Holes Spark Star Formation
By Robert Roy Britt
Senior Science Writer
posted: 07 February 2005
06:40 am ET

http://www.space.com/scienceastronomy/mystery_monday_050207.html

New observations portray black holes as Jekyll and Hyde characters. They can be creators as well as destroyers.

The classic view of black holes conjures images of gas and stars and even light being swallowed. That's why they're black. But when black holes feed, they create powerful high-speed jets that race at nearly light-speed into surrounding space.

Like a jolt of electricity breathing life into Frankenstein's monster, a black hole's jets can ignite star formation.

Wil van Breugel and Steve Croft of the Lawrence Livermore National Laboratory studied one of these jets slicing through a puzzling region of intense star formation known as Minkowski's Object. The jet, they say, caused a dense gas cloud to collapse and trigger the star birth.

The finding meshes nicely with a growing body of evidence suggesting black holes are integral players in galaxy formation.

Fiction to fact

"Some 20 years ago this kind of thinking was thought to be science fiction," van Breugel said. "It brings poetic justice to black holes because we think of them as sucking things in, but we've shown that when a jet emits from a black hole, it can bring new life by collapsing clouds and creating new stars."

Minkowski's Object is near a galaxy known as NGC 541. The galaxy's central black hole acts like a giant dynamo, accelerating globs of superheated matter and shooting them out along the axis of rotation. The jets are invisible, but astronomers have detected them with radio telescopes.

In a telephone interview, Croft explained what's going on.

The radio jet plows into a cloud of nearby gas in a supersonic shock wave, compressing and heating the gas. Gas in the cloud becomes ionized, meaning the atoms have lost electrons. After the shock passes, the ions recombine, creating radiation, which transports energy out of the cloud, Croft explained.

The cooling causes the cloud to contract still further, and when a knot of gas becomes dense enough, it can collapse to form a star.

More to learn

It is not clear how big a role all this plays in galaxy formation. Stars can form without a radio jet around to shock a cloud. Exploding stars known as supernovas, for example, can trigger new star formation.

Other studies show black holes play an important role in overall galaxy formation. "The formation of massive black holes is critical to the formation of new galaxies," Croft said.

Most large galaxies have a central black hole, and often they emit jets of high-speed material.

In the first few billion years after the Big Bang, when things were more crowded and chaotic, black hole jets probably triggered star formation in many nascent galleries, the researchers now believe.

"In the early universe this process may be important because the galaxies are still young, with lots of hydrogen gas but few stars, and the black holes are more active," van Breugel said.

Observations for the study were made with the National Radio Astronomy Observatory's Very Large Array, the Keck telescopes in Hawaii and the Hubble Space Telescope. The study was presented last month at a meeting of the American Astronomical Society.

This article is part of SPACE.com's weekly Mystery Monday series.

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