The SZ effect: Big black holes can block new stars

Elliptical galaxy NGC 1132, as seen by NASA's Chandra X-Ray Observatory; the blue/purple in the image is the X-ray glow from hot, diffuse gas that is not forming into stars. 

Credit: NASA, ESA, M. West (ESO, Chile), and CXC /Penn State University /G. Garmire, et al.

Massive black holes spewing out radio-frequency-emitting particles at near-light speed can block formation of new stars in aging galaxies, a study has found.

The research provides crucial new evidence that it is these jets of "radio-frequency feedback" streaming from mature galaxies' central black holes that prevent hot free gas from cooling and collapsing into baby stars.

"When you look into the past history of the universe, you see these galaxies building stars," said Tobias Marriage, assistant professor of physics and astronomy at Johns Hopkins and co-lead author of the study.

"At some point, they stop forming stars and the question is: Why? Basically, these active black holes give a reason for why stars stop forming in the universe."

The findings have been published in the journal Monthly Notices of the Royal Astronomical Society.

They were made possible by adaptation of a well-known research technique for use in solving a new problem.

Johns Hopkins postdoctoral fellow Megan Gralla found that the Sunyaev–Zel'dovich effect signature, typically used to study large galaxy clusters, can also be used to learn a great deal about smaller formations.

The SZ effect occurs when high-energy electrons in hot gas interact with faint light in the cosmic microwave background, light left over from earliest times when the universe was a thousand times hotter and a billion times denser than today.

"The SZ is usually used to study clusters of hundreds of galaxies but the galaxies we're looking for are much smaller and have just a companion or two," Gralla said.

"What we're doing is asking a different question than what has been previously asked," Gralla said.

"We're using a technique that's been around for some time and that researchers have been very successful with, and we're using it to answer a totally different question in a totally different subfield of astronomy."

"I was stunned when I saw this paper, because I've never thought that detecting the SZ effect from active galactic nuclei was possible," said Eiichiro Komatsu, director of the Max Planck Institute for Astrophysics in Germany and an expert in the field who was not involved in the research.

"I was wrong. ... It makes those of us who work on the SZ effect from galaxy clusters feel old; research on the SZ effect has entered a new era."

In space, hot gas drawn into a galaxy can cool and condense, forming stars. Some gas also funnels down into the galaxy's black hole, which grows together with the stellar population.

This cycle can repeat continuously; more gas is pulled in to cool and condense, more stars begin to shine and the central black hole grows more massive.

But in nearly all mature galaxies, the big galaxies called "elliptical" because of their shape – that gas doesn't cool any more. "If gas is kept hot, it can't collapse," Marriage said. When that happens: No new stars.

Marriage, Gralla and their collaborators found that the elliptical galaxies with radio-frequency feedback, relativistic radio-frequency-emitting particles shooting from the massive central black holes at their center at close to the speed of light, all contain hot gas and a dearth of infant stars.

That provides crucial evidence for their hypothesis that this radio-frequency feedback is the "off switch" for star-making in mature galaxies.

Marriage said, however, that it is still not known just why black holes in mature elliptical galaxies begin to emit radio-frequency feedback.

"The exact mechanism behind this is not fully understood and there are still debates," he said.

Komatsu said that the new Johns Hopkins-led study, combined with others detecting SZ signals from more ordinary galaxies, "pose new challenges to the theory of galaxy formation, as there were hardly any data which told us how much hot gas there is around galaxies."

More information: Monthly Notices of the Royal Astronomical Society, mnras.oxfordjournals.org/content/445/1/460.full

Pentagon trying to block construction of GLONASS stations in US

The US Department of Defense and Central Intelligence Agency have been trying to persuade the US State Department not to allow Roscosmos to build several GLONASS ground-based measuring stations in the United States, alleging that they could be used for military purposes.

They fear that the structures could help Russia spy on the United States and improve the precision of Russian weaponry, the officials said.

These monitor stations, the Russians contend, would significantly improve the accuracy and reliability of Moscow's version of the Global Positioning System, the American satellite network that steers guided missiles to their targets and thirsty smartphone users to the nearest Starbucks.

The Pentagon argues that if the State Department sanctions the GLONASS station deployments, Russia might be able to increase the accuracy of its guided missiles and could also use them for intelligence activity from inside US borders.

The arguments have prompted the White House to postpone decision-making on the issue until Russia provides further information, according to anonymous sources in the US Administration and Department of State.

US congressman Michel Rogers, who earlier requested the Pentagon's estimates of the consequences of deploying GLONASS stations for US national security, said he didn't understand why the US should be interested in encouraging GLONASS, a competitor to the American GPS system, when the use of GPS worldwide gives the US obvious advantages in many respects.

Moscow rejects the suggestion that the structures have anything to do with surveillance operations, contending they are designed to improve the accuracy of Russia's version of the Global Positioning System (GPS), the American satellite network that steers guided missiles to their targets and helps with navigation.

"They don't want to be reliant on the American system and believe that their systems, like GPS, will spawn other industries and applications," said a former senior official in the State Department's Office of Space and Advanced Technology.

The monitor stations have been a high priority for Russian President Vladimir Putin for several years as a means of improving Glonass, not just to benefit the Russian military and civilian sectors but also to compete globally with GPS.

Earlier this year, Russia positioned a Glonass station in Brazil and agreements with Spain, Indonesia and Australia are expected soon, according to Russian news reports. The United States has stations around the world but none in Russia.

In May 2012, Moscow requested that the United States allow the ground-monitoring stations on American soil.

American technical and diplomatic officials have met several times to discuss the issue and have asked Russian officials for more information, said Ms. Harf, the State Department spokeswoman.