Nav: Home

Quasar outburst revises understanding of universe, quasars

December 15, 2015

"On April 20, 2015, we got word from the Fermi satellite and the MAGIC telescope observatory that they had spotted a very active source -- one that was getting very bright in gamma rays," said Manel Errando, PhD, research scientist in physics in Arts & Sciences at Washington University in St. Louis. "At the time, I was chair of the committee at VERITAS that decides which sources we'll observe.

"We decided to give it a go."

VERITAS is a telescope array in southern Arizona that is sensitive to very high-energy gamma rays, those with billions of times more energy than the photons to which our eyes are sensitive.

Over the next 10 days, VERITAS detected high-energy gamma rays from this source, known as PKS 1441+25, including some with energies of about 200 GeV.

"We knew that this source emitted low-energy gamma rays, but this time we detected high energy ones that usually don't make it to Earth," Errando said.

"This is the first puzzle: how is it possible that gamma rays of such high energies made the trip all the way from this very distant quasar to Earth without getting lost in the fog of visible photons in between?

"The second puzzle was that the high-energy gamma rays were produced far from the black hole that powers them, not close to it, as you would expect," Errando said.

Errando is corresponding author on a paper about gamma ray observations of the flare that appeared in The Astrophysical Journal Letters Dec. 15, 2015. It is one of several simultaneous releases, he said.

"Everyone who had a telescope was looking at PKS 1441+25, which was active across all wavelengths," Errando said.

A fog of photons

"We were surprised to detect high-energy gamma rays," Errando said, "because they don't usually make it through. It's like turning on your high-beams in a fog."

Very energetic gamma rays are easily knocked off by visible light, the light from galaxies and stars that fills intergalactic space, he said. Lower-energy gamma rays mainly interact with ultraviolet light and X-rays. There are lots of sources of visible photons -- stars and galaxies -- but not as many X-ray sources that would bother the lower-energy gamma rays.

The arrival of high-energy gamma rays therefore allowed the astronomers to set a limit on the density of the fog of photons between the quasar and Earth, the photons that should make it difficult for those gamma rays to propagate.

Because it takes light time to travel, astronomy can be a time machine; the farther away the source, the farther back in time the light was emitted. The light from PKS 1441+25 traveled at least 7.6 billion years to reach Earth, or more than half of the age of the Universe.

The measurement VERITAS made validated theoretical models for the number and brightness of stars and galaxies in the universe going back in time 7.6 billion years, Errando said, leaving little room for the discovery of other sources that might be emitting optical light.

For example, he said, many people have been looking for what are called population III stars. Stars are sometimes described by their metal content, which provides a rough measure of their age. Population I stars condensed from gas seeded with heavy elements formed in previous giant stars. Population II stars formed in regions where there were no heavy-element producing predecessors. Population III stars, if they exist, would be stars that formed even earlier, before galaxies formed.

"The fact that the gamma rays get through means that there is not as much fog as you go farther out, and therefore any unconventional population of early galaxies and stars must not be very numerous," Errando said.

Action at a distance

While VERITAS was looking at the gamma ray emission from PKS 1441+25, the Owens Valley Radio Observatory in Bishop, Calif., was looking at its radio emission.

"Whenever we see radio waves, we assume they are coming from far away from the black hole," Errando said. "If they are created in a very dense environment, they are immediately absorbed. Only when the density gets low enough are they able to propagate outward. So we knew that the radio emission was coming from far up the jet, quite far away from the black hole."

Also, he said, the radio emission was changing quite a bit, getting brighter and weaker. All quasars emit at radio frequencies, but usually this emission is stable; the radio flux doesn't change that much.

What's more, fluctuations in the gamma-ray emission were synchronized with those in the radio emission. "The most likely explanation for the synchronization," he said, "is that the radio waves and gamma rays were emitted from the same region of the jet.

"That surprised me," Errando said. "The central black hole is the most energetic element in this whole system, so you would expect these very- high-energy gamma rays to be produced close to it. Instead, they were emitted roughly four light years away, roughly the distance from Earth to the nearest star.

"If the black hole were as big as a university classroom," he said, "the gamma rays would be emitted in Alaska.

He said one mechanism that could explain this is shocks. "When the wind of particles streams out of the black hole, it slams into an environment that's not moving, creating shock waves," Errando said. "It's probably these shock waves that are producing gamma rays so far away from the black hole.

"This tells us that the shocks in the particle winds are probably much more efficient than we had realized, because they are able to transport energy from the black hole great distances and still accelerate particles to these insane energies," he said.

"PKS 1441+25 is the first quasar in which we've seen this separation," he said. "If it is common, it might mean that quasars as a group make a bigger contribution to the total high-energy radiation power in the universe, because they're producing gamma rays and energetic particles that are able to escape to space.

"In any case, it's just spectacular that something as small as a black hole can drive energy transport to such great distances," Errando said.
-end-


Washington University in St. Louis

Related Black Hole Articles:

Scientists make waves with black hole research
Scientists at the University of Nottingham have made a significant leap forward in understanding the workings of one of the mysteries of the universe.
Collapsing star gives birth to a black hole
Astronomers have watched as a massive, dying star was likely reborn as a black hole.
When helium behaves like a black hole
A team of scientists has discovered that a law controlling the bizarre behavior of black holes out in space -- is also true for cold helium atoms that can be studied in laboratories.
Star in closest orbit ever seen around black hole
Astronomers have found evidence of a star that whips around a likely black hole twice an hour.
Tail of stray black hole hiding in the Milky Way
By analyzing the gas motion of an extraordinarily fast-moving cosmic cloud in a corner of the Milky Way, Astronomers found hints of a wandering black hole hidden in the cloud.
Hubble gazes into a black hole of puzzling lightness
The beautiful spiral galaxy visible in the center of the image is known as RX J1140.1+0307, a galaxy in the Virgo constellation imaged by the NASA/ESA Hubble Space Telescope, and it presents an interesting puzzle.
Clandestine black hole may represent new population
Astronomers have combined data from NASA's Chandra X-ray Observatory, the Hubble Space Telescope and the National Science Foundation's Karl G.
When will a neutron star collapse to a black hole?
Astrophysicists from Goethe-University Frankfurt have found a simple formula for the maximum mass of a rotating neutron star and hence answered a question that had been open for decades.
Behemoth black hole found in an unlikely place
Astronomers have uncovered a near-record breaking supermassive black hole, weighing 17 billion suns, in an unlikely place: in the center of a galaxy in a sparsely populated area of the universe.
Behemoth black hole found in an unlikely place
Astronomers have uncovered one of the biggest supermassive black holes, with the mass of 17 billion Suns, in an unlikely place: the centre of a galaxy that lies in a quiet backwater of the Universe.

Related Black Hole Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Bias And Perception
How does bias distort our thinking, our listening, our beliefs... and even our search results? How can we fight it? This hour, TED speakers explore ideas about the unconscious biases that shape us. Guests include writer and broadcaster Yassmin Abdel-Magied, climatologist J. Marshall Shepherd, journalist Andreas Ekström, and experimental psychologist Tony Salvador.
Now Playing: Science for the People

#513 Dinosaur Tails
This week: dinosaurs! We're discussing dinosaur tails, bipedalism, paleontology public outreach, dinosaur MOOCs, and other neat dinosaur related things with Dr. Scott Persons from the University of Alberta, who is also the author of the book "Dinosaurs of the Alberta Badlands".