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Re: Yahoo! News Story - Smallest Black Hole Found - Yahoo! News

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  • mahtezcatpoc
    http://chandra.harvard.edu/photo/2003/bhspin/ RA 17h 02m 49.50s | Dec -48º 47 23.00 (2000) 19 Sagittarius 42. Mark A. Holmes ... smallest
    Message 1 of 3 , Apr 6, 2008

      RA 17h 02m 49.50s | Dec -48º 47' 23.00" (2000)

      19 Sagittarius 42.

      Mark A. Holmes

      --- In thefixedstars@yahoogroups.com, "mahtezcatpoc"
      <mahtezcatpoc@...> wrote:
      > --- In thefixedstars@yahoogroups.com, Mark Andrew Holmes
      > <mahtezcatpoc@> wrote:
      > >
      > >
      > > Mark Andrew Holmes (mahtezcatpoc@) has sent you a news article.
      > > (Email address has not been verified.)
      > > ------------------------------------------------------------
      > > Personal message:
      > >
      > >
      > >
      > > Smallest Black Hole Found - Yahoo! News
      > >
      > > http://news.yahoo.com/s/space/20080401/sc_space/smallestblackholefound
      > BLGD...
      > Mark A. Holmes
      > Begin story.--
      > Smallest Black Hole Found
      > Andrea Thompson
      > Staff Writer
      > SPACE.com Tue Apr 1, 2:46 PM ET
      > NASA scientists have identified the smallest, lightest black hole yet
      > found.
      > The new lightweight record-holder weighs in at about 3.8 times the
      > mass of our sun and is only 15 miles (24 kilometers) in diameter.
      > "This black hole is really pushing the limits," said study team leader
      > Nikolai Shaposhnikov of NASA's Goddard Space Flight Center in
      > Greenbelt, Md. "For many years astronomers have wanted to know the
      > smallest possible size of a black hole, and this little guy is a big
      > step toward answering that question."
      > The low-mass black hole sits in a binary system in our galaxy known as
      > XTE J1650-500 in the southern hemisphere constellation Ara. NASA's
      > Rossi X-ray Timing Explorer (RXTE) satellite discovered the system in
      > 2001, and astronomers soon realized that the system harbored a
      > relatively lightweight black hole. But the black hole's mass had never
      > been precisely measured.
      > Black holes can't be seen, but they're identified by the activity
      > around them, which also helps astronomers estimate a size of the
      > region inside the activity, and how much mass must be in that confined
      > region to generate all the surrounding activity. More specifically,
      > astronomers can weigh black holes by using a relationship between the
      > apparent size of the black hole and the X-rays emitted by the torrent
      > of gas that swirls into the black hole's disk from its companion star.
      > As the gas piles up near the black hole, it "becomes very dense and
      > congested," like a traffic jam, Shaposhnikov said at a press
      > conference announcing the find. "So matter has to literally squeeze
      > into the black hole."
      > As it is squeezed, the gas heats up and radiates X-rays. The intensity
      > of the X-rays varies in a pattern repeated over a nearly regular
      > interval. Astronomers have long suspected that the frequency of this
      > signal, called the quasi-periodic oscillation, or QPO, depends on the
      > mass of the black hole.
      > As the black hole gets bigger, the zone of swirling gas is pushed
      > farther out, so the QPO ticks away slowly. But for smaller black
      > holes, the gas sits closer in and the QPO ticks rapidly.
      > Shaposhnikov and his colleague Lev Titarchuk of George Mason
      > University used this method to "weigh" XTE J1650-500 and found a mass
      > of 3.8 suns. This value is well below the previous record holder GRO
      > 1655-40, which tips the scales at about 6.3 suns.
      > This new �mass measurement could help shed light on what the
      > star that will produce a black hole is. Astronomers know that some
      > unknown critical threshold, possibly between 1.7 and 2.7 solar masses,
      > marks the boundary between a star that generates a black hole upon its
      > death and one that produces a neutron star.
      > "This new result brings us much closer to the theoretically predicted
      > limit," Shaposhnikov said.
      > Knowing this boundary would help scientists understand the behavior of
      > matter when it is scrunched to extraordinarily high densities.
      > "The question of black hole masses has concerned us for more than a
      > decade now," said astrophysicist Vicky Kalogera of Northwestern
      > University, who was not involved with the study, during the press
      > conference. Scientists had predicted that their should be more black
      > holes at the lower end of the mass range than astronomers had
      > identified, so this study helps clear up some confusion as to where
      > these lightweight black holes were, she added.
      > Kalogera did caution that the method used by Shaposhnikov and
      > Titarchuk is not the main way that black hole masses are measured, but
      > noted that their measurements of the masses of other black holes
      > agreed well with the results from the standard method.
      > Shaposhnikov and Titarchuk presented their findings on March 31 at the
      > American Astronomical Society's High-Energy Astrophysics Division
      > meeting in Los Angeles.
      > --End story.
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