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Illuminating a black hole

Researchers put together the most thorough look yet of the mass at the heart of the Milky Way.

December 10, 2008|John Johnson Jr. | Johnson is a Times staff writer.

After 16 years of research, teams of American and European scientists have compiled the most complete portrait of the gigantic black hole at the center of the Milky Way, plotting its gravity-bending mass as being equivalent to a staggering 4 million suns.

The researchers from Germany and UCLA also pinpoint the distance to the center of the galaxy at 27,000 light-years.

Neither figure differs markedly from previous estimates of the black hole's size and distance, but it is the most conclusive proof to date that our galaxy of billions of stars is indeed centered on an object of such tremendous power that it gobbles all light and matter that dares to venture into its neighborhood.

Reinhard Genzel, leader of the European team based at the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, said researchers had the best evidence yet that "supermassive black holes really do exist."

Andrea Ghez, leader of the UCLA Galactic Center Group, which has been engaged in what Ghez called a "useful rivalry" with the Europeans, said the results represented a more fully developed understanding of the galaxy's center than the guesses of the past.

"We had the luxury of ignorance. It's like we went from a teenager to an adult," she said.

Both research papers are scheduled to be published in upcoming issues of the Astrophysical Journal.

Since direct observation of a black hole is impossible, the two studies focused on a set of stars that orbit near the black hole.

The European team began its research in 1992 with the New Technology Telescope in La Silla, Chile, eventually shifting to the Very Large Telescope at the same site.

Ghez said her team has been using the giant Keck telescope in Hawaii.

By analyzing the velocity and size of the stars' orbits, the researchers were able to calculate the mass of the black hole and its distance.

Two distinct populations of stars reside in the heart of the galaxy. The stars in the innermost region, said Stefan Gillessen, the author of the European study, are in random orbits "like a swarm of bees."

Farther out, a group of stars orbit in a more orderly, disc-like pattern. Both teams have observed one star, known as S-02, long enough to see it make one complete revolution around the black hole.


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