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Astronomy Picture of the Day |
APOD: 1997 January 15 – Black Hole Signature From Advective Disks
Explanation:
What does a black hole look like? If alone,
a black hole
would indeed appear
quite black, but many black hole candidates are part of binary star systems.
So how does a black hole binary system
look different from a neutron star binary system?
The above drawings indicate it
is difficult to tell! Recent theoretical work,
however, has provided a new way to tell them apart: advective accretion flows (ADAFs).
A black hole system so equipped
would appear much darker than a similar neutron star
system. The difference is caused by the hot gas from the ADAF disk
falling through the event horizon
of the black hole and disappearing - gas that would have emitted
much light were the central object only a neutron star. Recent observations
of the soft X-ray transient
V404 Cyg
has yielded a spectrum
much like an ADAF onto a black hole
- and perhaps brighter than allowable from an ADAF onto a neutron
star.
APOD: 2004 2002 September 8 – Too Close to a Black Hole
Explanation:
What would you see if you went right up to a
black hole?
Above are two computer generated images
highlighting how strange things would look.
On the left is a normal star field containing the
constellation Orion.
Notice the three stars of nearly equal brightness that make up
Orion's Belt.
On the right is the same star field but this time with a
black hole superposed in the center of the frame.
The
black hole has such strong
gravity that light is noticeably bent towards it -
causing some very unusual
visual distortions.
In the distorted frame, every star in the normal frame
has at least two bright images - one on each side of the
black hole.
In fact, near the
black hole, you can see the whole sky -
light from every direction is
bent around and comes back to you.
Black holes are thought to be the densest state of matter,
and there is
indirect evidence for their presence in
stellar binary systems
and the centers of
globular clusters,
galaxies, and
quasars.
APOD: 2004 February 24 - X-Rays Indicate Star Ripped Up by Black Hole
Explanation:
What could rip a star apart?
A black hole.
Giant black holes in just the right mass range would
pull on the front of a closely passing star much more
strongly than on the back.
Such a strong tidal force would stretch out a star and
likely cause some of the star's gasses to fall into the black hole.
The infalling gas has been predicted
to emit just the same blast of
X-rays that have
recently been seen in the center of galaxy
RX J1242-11.
Above, an artist's illustration depicts the
sequence of destruction (assuming that
image-distorting gravitational-lens effects of the
black hole are somehow turned off).
Most of the stellar remains would be flung out into the galaxy.
Such events are rare, occurring perhaps only
one in 10,000 years for typical
black holes at the center of
typical galaxies.
Authors & editors:
Robert Nemiroff
(MTU) &
Jerry Bonnell
(USRA)
NASA Web Site Statements, Warnings, and
Disclaimers
NASA Official: Jay Norris.
Specific rights apply.
A service of:
EUD at
NASA /
GSFC
& Michigan Tech. U.