Observations from UF Camera deepen mystery about galaxy

October 30, 2001

GAINESVILLE, Fla. — 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 said.

“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 instruments.”