Expert sheds light on black holes

UC Irvine physics and astronomy professor Aaron Barth spoke at the university Tuesday morning about his team’s research on black holes.

His team has been responsible for the discovery of eight of what are believed to be some of the smallest known black holes in the universe.

“The basic idea of a black hole is it’s an object so dense and so concentrated that nothing can escape from its gravitational pull,” Barth said.

The black hole concept goes back to a letter written by British astronomer John Mitchell, who theorized about such an object in 1784.

Black holes are so dense that “if you wanted to turn the Earth into a black hole, you would have to compress the Earth to a diameter of 1 inch” while keeping its mass intact, Barth said.

“There are probably millions of black holes wandering around,” Barth said. “They’re very hard to count because we can’t see them.”

A small number of black holes can be seen and studied in great detail because of the light-emitting objects that orbit around them for millions of years, before eventually being sucked completely into the black hole.

A common example is a binary solar system, made of two stars that orbit each other. When one star collapses into a black hole, the outer layers of the companion star begins to stream into it. As the gases spiral into the center of the black hole, they can emit large quantities of X-ray wavelengths that can be spotted with X-ray telescopes, Barth said, adding that there are many likely such candidates within our galaxy alone.

In fact, he said, it has been confirmed that the an extremely compact object that has the mass of four of our suns is sitting at the center of the Milky Way galaxy, which all other bodies in the galaxy spin around.

The question now is whether that object is a black hole; given the laws of physics as we know them, a black hole is the only real option.

Astronomers use Doppler shift principals to determine the mass of a black hole. A common example of the Doppler shift in everyday life is the way that an approaching ambulance siren sounds louder as it approaches and then rapidly declines in volume as it passes.

“Light behaves in exactly the same way,” Barth said. Distance, speed and then mass can be determined through characteristic dips and rises of light.

Many such black holes turn out to have the mass of five to 20 of our suns. Supermassive black holes, however, can be many billions of times more massive.

One discovered recently by the University of Texas, thought to be the largest known, has 6 billion times more mass than our solar system’s sun.

Quasars, super-bright objects that are believed to surround supermassive black holes in the centers of galaxies, also can indicate the black holes’ presence.

“Some of the brightest quasars can be thousands of times brighter than entire galaxies,” Barth said. The most distant quasars may be evidence of massive black holes formed during the earliest epochs of the universe. Light from the most distant known quasar takes 12.8 billion years to reach Earth; its black hole is thought to be 3 billion solar masses.

Barth and his team hope to locate and find small black holes to learn how such supergiants got their start. One of his graduate students found one that was only the mass of 300,000 suns — extremely small by astronomical standards.

About 30 astronomers in a group put together by Barth’s team were given 64 continuous nights to search for small black holes in 2008.

“Nothing like that had ever been done before,” he said.

They discovered eight previously unknown quasars in their hunt, and now hope to understand how black holes and quasars influenced the formation of galaxies.

They’ll have two new tools in the future: an 8-meter telescope in Chile and a 30-meter telescope, the largest ever constructed, that will be built in Hawaii.

The lens will roughly be the size of Angel Stadium’s infield. It’s expected to go live in 2018, and could yield the deepest glimpses ever into the most distant galaxies.

“It’s a tremendously exciting prospect,” Barth said.