An international team of astronomers, including several members from Iowa State, has helped discover a new class of active galaxies.

These galaxies, called Blazars, have the shortest gamma ray wavelengths. They are among the brightest objects in the sky. Observed for the first time in 1995, the Blazar Markarian 501 is thought to be powered by a massive black hole.

Four American universities and several overseas universities were involved in the project, said Richard Lamb, ISU professor of physics and astronomy. To find Markarian 501, the researchers used arrays of light detectors and mirrors, set up on a mountain top in southern Arizona.

In 1992, the same team of researchers detected the first extragalactic source of very-high-energy gamma rays, from the galaxy Markarian 421. Markarian 501’s gamma rays are even higher in energy.

“One distinction [between Markarian 421 and Markarian 501] is that there is a gamma ray telescope aboard a satellite which has detected a number of objects like this at lower energies,” said David Carter-Lewis, ISU professor of physics and astronomy.

“Markarian 421 was detected at a lower energy by the satellite. Markarian 501 was not detected [by this satellite],” he said.

“It’s interesting that both these objects are relatively close to the Milky Way — our galaxy,” said Carter-Lewis. “Markarian 421 was only seen relatively weakly by the satellite.” But it was easy to see from the ground, he added.

Gamma rays are extremely narrow beams of very high energy particles.

“A gamma ray is a packet of electromagnetic waves — the smallest packet of electromagnetic energy,” Lamb said.

“Gamma waves are the shortest waves,” Lamb said. “These waves are smaller than the nucleus of an atom, with extremely high oscillation. Our gamma rays are one trillion times more energetic than the electromagnetic waves from the sun. They are the finger print of charged particles that have even higher energy,” Lamb said.

The frequency of gamma rays is 1,000 times that of X-rays, and the gamma rays produced by Markarian 501 are extremely strong, Lamb said. This implies that Markarian 501 and galaxies like it are actually natural particle accelerators on a scale that had not been thought possible, he added.

“We’re beginning to see a whole new class of sources. These are active galactic nuclei that have massive black holes at the center. They swallow mass and convert it to energy. It comes out as very fast particles spurting out as jets,” Lamb said.

“The jet is pointed pretty much directly at us, so we’re kind of looking down the barrel of a gun, if you please,” he said.

Because the particles that make up gamma rays travel in the form of narrow beams, detection depends on the chance that an emitting galaxy is aimed directly at the solar system.

Smithsonian physicist and collaborator James Buckley said there may be many more galaxies like Markarian 501. If so, we may not be seeing them because they are not pointed our way.

“If you see gamma rays then there are electrons and protons at higher energies. These are injected into the atmosphere,” Lamb said.

“What this points to is an intergalactic absorption of gamma rays at very high energies,” Carter-Lewis said. “Intergalactic absorption of gamma rays was a mechanism proposed long ago in which gamma rays collide with infrared light between the galaxies and in this collision form pairs of electrons and positrons.”

This collision is responsible for the creation of matter, Carter-Lewis said.

“It’s been a long 80-year mystery as to where these cosmic rays come from and I think we’re beginning to understand that mystery,” Lamb said.