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News Release

June 18, 2004



'Blazar' illuminates era when stars and galaxies formed


"In cosmology, it turns out that 'a galaxy a long time ago' and 'far, far away' really do go together," says Associate Professor Roger Romani, who with graduate student David Sowards-Emmerd and Professor Peter Michelson of Stanford, and radio astronomer Lincoln Greenhill of the Harvard-Smithsonian Center for Astrophysics, spotted one of the oldest supermassive black holes yet found. The scientists collaborate at the Kavli Institute for Particle Astrophysics and Cosmology at Stanford. "In this case, we're looking at [a black hole] far enough away that it's within a billion years of the origin of it all, the Big Bang."

The supermassive black hole sits in the center of a galaxy. A disk of stars and gas swirl around the black hole and eventually get sucked in. "That generates enormous amounts of power, enormous amounts of energy," Romani says. "It's far more efficient even than nuclear fusion. These gravity--powered sources are the most powerful sources in the universe."

As black holes go, this one is a messy eater. It's Jabba the Hutt, in fact, gobbling up its galaxy so quickly that not everything is making it down its throat past the point of no return -- that place, called the "event horizon," where not even light can escape gravity's strongest pull. The matter that doesn't make it past the event horizon is spewing back up in the form of accelerated high-energy particles.

If a black hole amid a galaxy shoots out high-energy particles in narrow jets that just happen to be aimed at Earth, astrophysicists give the whole thing a special name -- "blazar." Amazingly, these blazars can be detected at nearly all energies, even at the high energy of gamma rays. In fact, distant blazars seem to dominate the gamma-ray sky and can obscure other objects of interest. Pulsars, spinning neutron stars nearby in our own galaxy, can also emit gamma rays, but far fewer of them are known. Romani, whose main interest is pulsars, wanted to identify and discard blazars so he could concentrate on the neutron stars.



"Something really new is waiting to be found in the gamma-ray sky," Romani says. "If we could identify all the blazars, tag the pulsars -- the things that are left over, that's where the really new discoveries will be."

Blazar hunting


Greenhill led the effort to obtain radio images of the blazar jet using the Very Long Baseline Array (VLBA). Funded by the National Science Foundation and operated by the National Radio Astronomy Observatory, the VLBA is essentially a radio camera. It consists of 10 dish antennas -- 25 meters wide and distributed from Hawaii across the United States to St. Croix -- slaved together with computers to create a composite image with a resolution Greenhill calls "comparable to what they would get with a single antenna about as large as a continent."

To find out how far away the blazar was, Romani and Sowards-Emmerd used the Hobby-Eberly Telescope (HET), an optical instrument in a remote part of Texas, to obtain spectral patterns of visible and infrared light. HET is a joint project of the University of Texas at Austin, Pennsylvania State University, Stanford, Ludwig-Maximilians-Universit?t M?nchen and Georg-August-Universit?t G?ttingen.


The red shift corresponds to age. "The higher that number, the smaller the universe was when the light was emitted -- hence, the earlier you're talking about," Romani explains.







"What's interesting about a billion years after the Big Bang is that this marks the end of the 'Dark Age,'" Romani says. "The universe first formed with an enormous flash of light and heat -- that's the Big Bang -- and then cooled off. And everything's dark for about a billion years. And toward the end of that period, the first stars and black holes and galaxies start collapsing and forming and turning on. We talk about that as the end of the Dark Age. So it's very interesting, and this is one of the big pushes in cosmology, to find objects back in the tail end of the Dark Age, when things are first lighting up, and then to use those to figure out how everything we have in the universe formed."

Extreme physics

In the next year, the scientists hope to use the VLBA to take a better picture of the jet detected with radio waves and then observe its X-ray spectrum. This will help illuminate the matter between the supermassive black hole and Earth, clarify the black hole's size and characterize the jet's material as it moves away from the black hole at nearly the speed of light.

"Studying these things gives us a window into the sort of physical processes that we can't yet control here on Earth," Romani says. "They're the extremes of physics."

Those extremes fascinate Romani. "Pulsars are, I think, the most extreme objects in our universe," he says. These cores of dead stars have collapsed, but not far enough to form an event horizon, so they are just short of turning into black holes. They are the densest things in the measurable universe. They have the strongest magnetic fields. Their surfaces have extremely high temperatures. They are cosmic accelerators that speed particles to the highest energies known.

So far, scientists have found only a handful of gamma-ray pulsars, and Romani is particularly excited about GLAST as a means of hunting down more in the Milky Way.

"I'm particularly interested in ways in which you could find extreme physics out there in the cosmos and get a handle on physics of the 22nd or 23rd century by seeing what's going on in the sky."


Editor Note:

A photo of the researchers is available at

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