UCLA astronomers take space-breaking photograph
By Jennifer Lauren Lee
Oct. 20, 2002 9:00 p.m.
The center of the galaxy never looked so good.
UCLA astronomers and their colleagues recently released the
highest-resolution mid-infrared picture ever taken of the center of
our Milky Way galaxy.
The photos reveal details about the bizarre phenomena
surrounding a massive black hole in the middle of our galaxy.
The team, led by UCLA professor of astronomy Dr. Mark Morris,
took the picture at the Keck II telescope in Hawaii, using an
infrared camera built at NASA’s Jet Propulsion Laboratory.
The camera, called the Mid-Infrared Large-Well Imager, or MIRLIN,
created the multi-colored image of the center of the galaxy using
several different wavelengths of infrared light.
The images they took will help astronomers understand more about
the process of star formation and how black holes affect that
process ““ in our own galaxy and elsewhere in the
universe.
Astronomers have taken similar pictures of the galactic center
using other parts of the electromagnetic spectrum, according to
JPL’s Dr. Michael Ressler, who built the camera with Dr.
Michael Werner at JPL.
“Before, (the center of the galaxy) always looked smooth
and flat,” said Ressler. “Now, you can really see all
the knots and tendrils.”
MIRLIN was originally built as a “general-purpose
instrument” to be used to take mid-infrared pictures of the
sky by any team of astronomers who wanted to use it.
But Morris’ team chose to point it at the center of our
galaxy to see what would happen.
According to Morris, the mid-infrared part of the
electromagnetic spectrum corresponds with our perception of heat.
Each wavelength of light detected by the camera shows up as a
different color in the picture, allowing astronomers to “tell
which parts are hot and which are cold,” he explained.
Getting such a clear image of our galaxy when it is 25,000 light
years away is an amazing feat for an Earth-based camera, according
Dr. Andrea Ghez, also a professor of astronomy at UCLA and member
of the team that processed the MIRLIN image.
The Earth’s atmosphere absorbs much of the light traveling
through space (such as cancer-causing ultraviolet radiation),
preventing it from reaching the ground or astronomers’
detection equipment.
But certain wavelengths pass right through the gas surrounding
our planet. Morris’ team used the mid-infrared part of the
electromagnetic spectrum because it matches one of these
atmospheric windows.
Also, the 14,000-foot elevation of the Keck II telescope of
Hawaii makes it “by far one of the best telescopes in the
world,” according to graduate student Angelle Tanner, who
wrote her thesis on the MIRLIN project.
The telescope sits well above the clouds and weather that
obscure the views of many other ground-based telescopes.
“It’s amazing to me that we can beat our local
(Earth-based) background. You get a perfectly clean image without
having to go into space,” Ghez said.
In the center of the image is a monstrous black hole three
million times more massive than the sun. Although the black hole is
invisible at these wavelengths, this new picture clearly shows the
effects of its enormous gravitational pull on the surrounding stars
and dust.
Astronomers have long been aware of this phenomenon, but
“it’s striking to see what you expect is taking place
anyway,” Morris said.
Among the “striking” phenomena revealed by the
high-resolution MIRLIN image is a disc of dust, called the
“northern arm,” which is spiralling inward and
preparing to fall into the black hole.
“The dust hasn’t hit yet,” said Dr. Morris.
But when it does in a few thousand years, he continues, “it
will produce a cosmic fireworks show,” spewing out huge
amounts of energy as the black hole feeds on the viscous disc of
dust and gas.
According to Morris, the MIRLIN image has also detected
something mysterious hidden within the dust: a group of young,
luminous stars strung out “like lights on a Christmas
tree,” obscured from our view, but hot enough to warm the
dust around them, making it glow more brightly in the mid-infrared
and allowing MIRLIN to detect it.
Morris and his team know that these luminous stars are young
because brighter stars burn faster, rapidly consuming themselves.
But, he continued, “the tidal forces (of the black hole)
prevent stars from forming anywhere near it.”
In a cosmic game of tug-of-war, the black hole pulls each star
apart even as gravity works to pull it together.
So why are all these young stars located near the black hole at
the center of the galaxy?
Morris’ team does not have the answer, but “the IR
image (will help) us … find answers to these
questions.”
