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September 20, 2005 01:00 PM (EDT)

News Release Number: STScI-2005-26

Hubble Finds Mysterious Disk of Blue Stars Around Black Hole

September 20, 2005: Astronomers using NASA's Hubble Space Telescope have identified the source of a mysterious blue light surrounding a supermassive black hole in our neighboring Andromeda Galaxy (M31). Though the light has puzzled astronomers for more than a decade, the new discovery makes the story even more mysterious. The blue light is coming from a disk of hot, young stars that are whipping around the black hole in much the same way as planets in our solar system are revolving around the Sun. Astronomers are perplexed about how the pancake-shaped disk of stars could form so close to a giant black hole. Andromeda and its complex core can be seen in the illustration and two images [above]. The illustration [lower, right] shows the disk of blue stars nested inside a larger ring of red stars. The Hubble photo [upper, right] reveals Andromeda’s bright core. The image at left shows the entire galaxy.

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Q & A: Understanding the Discovery

  1. 1. How could the disk of blue stars have formed around the black hole?

  2. Astronomers do not know how the blue stars could have formed around the black hole. The stars are massive and have short life spans, so astronomers do not think they coincidentally witnessed a once-in-a-lifetime event. They think the mechanism that created the disk of stars probably formed other disks in the past and will trigger the formation of similar disks in the future.

  3. 2. Will the stars fall into the black hole?

  4. The stars will not fall into the black hole because they are in orbit around it, just as our Earth will not plummet into our Sun because it revolves around our star. The black hole's intense gravitational grip means that the stars must orbit very fast.

  5. 3. Do other galaxies have blue stars in their cores?

  6. Astronomers have seen blue light in the cores of other spiral galaxies. Even our Milky Way Galaxy has a cluster of blue stars at its core. Finding blue stars in the cores of two neighboring galaxies, Andromeda and the Milky Way, suggests that other galaxies may have them.

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Credit: NASA, ESA, R. Bender (Max Planck Institute for Extraterrestrial Physics), T. Lauer (NOAO), and J. Kormendy (University of Texas)