Press Release

Observations from U.Florida camera deepen mystery about galaxy

By SpaceRef Editor
November 1, 2001
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A surprising discovery that a fundamental feature
normally surrounding a black hole is missing may revolutionize scientific
understanding of active galaxies, say University of Florida researchers.

The absence of a signature doughnut-shaped ring of dusty material
surrounding the massive black hole in the popularly studied M87 galaxy
is making scientists rethink some of their theories, said James Radomski,
a graduate student in UF’s astronomy department and member of the
groundbreaking team.

Scientists anticipated that the dusty ring, which fundamentally affects
our view of the nuclear cauldron in such active galaxies, would be easy
to observe with new instruments on the largest telescopes. To their
surprise, they found nothing in their latest observations.

The results of the study appear in this week’s issue of The Astrophysical
Journal. Other team members include lead researcher Eric S. Perlman, a
physicist at the University of Maryland-Baltimore County; UF astronomy
professors Chris Packham and Robert Pina; and R. Scott Fisher, a
scientist with the Gemini Observatory and a recent UF doctoral graduate.

“It’s more of a puzzle on what we didn’t find as opposed to what we
actually found,” Radomski said. “Not seeing something we expected to
see is making us rethink the entire accepted theory of how these active
galaxies work and what’s powering their emissions.”

The doughnut-shaped ring, called a torus, is either missing or extremely
faint, Radomski said. The observations show that all the emission the
team observed can be explained as part of a huge jet coming out of the
region surrounding the black hole at the heart of the galaxy, he said.

The torus should have been easy to detect because the midinfrared images
of the galaxy’s center are the deepest and sharpest ever captured at
these wavelengths, Packham said. The combination of the giant 8.1-meter
Gemini North Telescope, one of the world’s largest telescopes, on
Hawaii’s Mauna Kea, and UF’s midinfrared image/spectrometer permit such
groundbreaking observations to be made, he said.

The M87 galaxy is something of a “prototype galaxy” for astronomers to
test their theories because, despite being 50 million light years from
Earth, it is one of the closest galaxies of its type, Packham said.
When the Hubble telescope was launched, M87 was one of the first
objects in the universe it looked at, he said.

Named by the amateur astronomer Charles Messier because it was the 87th
object he catalogued in the sky, M87 is what’s known as an active
galactic nucleus. This kind of galaxy has an incredibly high-energy
beam of particles jetting from the center of a large black hole called
a “super-massive black hole,” he said.

The area at the center contains the mass of about 3 billion stars
compressed into a region about the size of our solar system, Packham

“Can you imagine putting out more energy in an area that is about the
size of a solar system than from the billions of stars that make up
the whole galaxy put together?” he said. “Only a small percentage of
galaxies are like this.”

Astronomers believed the torus of dusty material surrounding the black
hole was responsible for shaping the way we observe the powerful nuclear
emission, Packham said. The torus absorbs high-energy radiation coming
from the region around the black hole and helps create a huge jet, all
fueled by gas and dust, he said.

“The torus has been such a key part in the accepted model of these
active galactic nucleus galaxies,” Radomski said. “We may have to revise
our understanding of this class of galaxies.”

The next step for researchers will be to study other galaxies to see
if the lack of a visible torus is a general trend or peculiar to this
particular galaxy, he said.

Fisher predicts that in the next five years astronomers are likely to
make many more discoveries like that of the torus of M87 as a result
of advances in modern technology.

“The new instruments and telescopes are revolutionizing the way we
think about astronomy,” he said. “These observations of M87 were really
made possible because we’re at this cusp of the next generation of

SpaceRef staff editor.