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

NASA WISE survey finds thousands of new stars, but no 'Planet X'

A nearby star stands out in red in this image from the Second Generation Digitized Sky Survey (DSS). 

Image credit: DSS /NASA/JPL-Caltech

After searching hundreds of millions of objects across our sky, NASA's Wide-Field Infrared Survey Explorer (WISE) has turned up no evidence of the hypothesized celestial body in our solar system commonly dubbed "Planet X."

Researchers previously had theorized about the existence of this large, but unseen celestial body, suspected to lie somewhere beyond the orbit of Pluto.

In addition to "Planet X," the body had garnered other nicknames, including "Nemesis" and "Tyche."

This recent study, which involved an examination of WISE data covering the entire sky in infrared light, found no object the size of Saturn or larger exists out to a distance of 10,000 astronomical units (au), and no object larger than Jupiter exists out to 26,000 au.

One astronomical unit equals 93 million miles. Earth is 1 au, and Pluto about 40 au, from the Sun.

Kevin Luhman

"The outer solar system probably does not contain a large gas giant planet, or a small, companion star," said Kevin Luhman of the Center for Exoplanets and Habitable Worlds at Penn State University, author of a paper 'A SEARCH FOR A DISTANT COMPANION TO THE SUN WITH WISE' in the Astrophysical Journal describing the results.

But searches of the WISE catalogue are not coming up empty. A second study reveals several thousand new residents in our Sun's "backyard," consisting of stars and cool bodies called brown dwarfs.

Ned Wright

"Neighbouring star systems that have been hiding in plain sight just jump out in the WISE data," said Ned Wright of the University of California, Los Angeles (UCLA), the principal investigator of the mission.

WISE survey finds thousands of new stars, but no 'Planet X'

Data from NASA's WISE, has found no evidence for a hypothesized body sometimes referred to as "Planet X." 

Credit: Penn State University

The second WISE study, which concentrated on objects beyond our solar system, found 3,525 stars and brown dwarfs within 500 light-years of our Sun.

Davy Kirkpatrick

"We're finding objects that were totally overlooked before," said Davy Kirkpatrick of NASA's Infrared and Processing Analysis Center (IPAC) at the California Institute of Technology, Pasadena, Calif.

Kirkpatrick is lead author of the second paper, also in the Astrophysical Journal.

Some of these 3,525 objects also were found in the Luhman study, which catalogued 762 objects.

The WISE mission operated from 2010 through early 2011, during which time it performed two full scans of the sky, with essentially a six-month gap between scans.

The survey captured images of nearly 750 million asteroids, stars and galaxies. In November 2013, NASA released data from the AllWISE program, which now enables astronomers to compare the two full-sky surveys to look for moving objects.

In general, the more an object in the WISE images appears to move over time, the closer it is. This visual clue is the same effect at work when one observes a plane flying low to the ground versus the same plane flying at higher altitude.

Though traveling at the same speed, the plane at higher altitude will appear to be moving more slowly.

Searches of the WISE data catalogue for these moving objects are uncovering some of the closest stars.

The discoveries include a star located about 20 light-years away in the constellation Norma, and as reported last March, a pair of brown dwarfs only 6.5 light-years away, making it the closest star system to be discovered in nearly a century.

Despite the large number of new solar neighbors found by WISE, "Planet X" did not show up.

Previous speculations about this hypothesized body stemmed in part from geological studies that suggested a regular timing associated with mass extinctions on Earth.

The idea was that a large planet or small star hidden in the farthest reaches of our solar system might periodically sweep through bands of outer comets, sending them flying toward our planet.

The Planet X-based mass extinction theories were largely ruled out even prior to the new WISE study.

WISE survey finds thousands of new stars, but no 'Planet X'

The third closest Binary star system to the sun, called WISE J104915.57-531906, is at the center of the larger image, which was taken by NASA's WISE. 

Credit: NASA /JPL /Gemini Observatory /AURA /NSF

Other theories based on irregular comet orbits had also postulated a Planet X-type body.

The new WISE study now argues against these theories as well.

Both of the WISE searches were able to find objects the other missed, suggesting many other celestial bodies likely await discovery in the WISE data.

"We think there are even more stars out there left to find with WISE. We don't know our own sun's backyard as well as you might think," said Ned Wright.

WISE was put into hibernation upon completing its primary mission in 2011.

In September 2013, it was reactivated, renamed NEOWISE and assigned a new mission to assist NASA's efforts to identify the population of potentially hazardous near-Earth objects.

NEOWISE will also characterise previously known asteroids and comets to better understand their sizes and compositions.

New Stars surrounded by Protoplanetary Gaseous Disks

Many newly formed stars are surrounded by what are called protoplanetary disks, swirling masses of warm dust and gas that can constitute the core of a developing solar system.

Proof of the existence of such disks didn't come until 1994, when the Hubble telescope examined young stars in the Orion Nebula.

Protoplanetary disks may potentially become celestial bodies such as planets and asteroids but just how they make that transformation will remain a mystery to science until researchers can get a grasp on the disordered movement, or turbulence, that characterizes the constituent gases of the disks.

Turbulence is what some people regard as "the last great classical physics problem."

"By understanding the nature of the gases, we can learn something about how small particles interact with each other, coagulate to become larger particles and then ultimately form planets," says Jake Simon of the University of Colorado, principal investigator of a research project currently taking on two primary challenges in the quest to understand protoplanetary disk turbulence.

"In a particular region in these disks, the electrons are tied to magnetic fields, while the ions are not. This leads to something called the Hall effect and currently, our numerical algorithms cannot accurately capture the nature of this effect," he says.

Edwin Hall

Discovered by American physicist Edwin Hall in 1879, the Hall effect refers to a voltage-difference that occurs across an electrical conductor.

The voltage difference is crossways to an electrical current in the conductor and a magnetic field that is perpendicular to the current.

"If the ions and electrons don't collide with the neutrals frequently enough, ambipolar diffusion acts to damp out the turbulence," he says.

"The degree to which this happens has been explored with our high-resolution numerical simulations that we have run on the Kraken supercomputer. We believe we now have a much better understanding of how disks behave in their outer regions, far from the central star."

KRAKEN SuperComputer


The National Science Foundation's Extreme Science and Engineering Discovery Environment (XSEDE) has provided the compute time allocation for the project on Kraken, one of the most powerful supercomputers in academia.

Kraken is housed at Oak Ridge National Laboratory and managed by the University of Tennessee's National Institute for Computational Sciences.

Read more about Stellar Chemistry here: Stellar Chemistry