Posted on by Jason Major

What Happens When Supermassive Black Holes Merge?

Frame from a simulation of the merger of two black holes and the resulting emission of gravitational radiation (NASA/C. Henze)

The short answer? You get one super-SUPERmassive black hole. The longer answer?

Well, watch the video below for an idea.

This animation, created with supercomputers at the University of Colorado, Boulder, show for the first time what happens to the magnetized gas clouds that surround supermassive black holes when two of them collide.

The simulation shows the magnetic fields intensifying as they contort and twist turbulently, at one point forming a towering vortex that extends high above the center of the accretion disk.

This funnel-like structure may be partly responsible for the jets that are sometimes seen erupting from actively feeding supermassive black holes.

The simulation was created to study what sort of “flash” might be made by the merging of such incredibly massive objects, so that astronomers hunting for evidence of gravitational waves — a phenomenon first proposed by Einstein in 1916 — will be able to better identify their potential source.

Read: Effects of Einstein’s Elusive Gravity Waves Observed

Gravitational waves are often described as “ripples” in the fabric of space-time, infinitesimal perturbations created by supermassive, rapidly rotating objects like orbiting black holes. Detecting them directly has proven to be a challenge but researchers expect that the technology will be available within several years’ time, and knowing how to spot colliding black holes will be the first step in identifying any gravitational waves that result from the impact.

In fact, it’s the gravitational waves that rob energy from the black holes’ orbits, causing them to spiral into each other in the first place.

“The black holes orbit each other and lose orbital energy by emitting strong gravitational waves, and this causes their orbits to shrink. The black holes spiral toward each other and eventually merge,” said astrophysicist John Baker, a research team member from NASA’s Goddard Space Flight Center. “We need gravitational waves to confirm that a black hole merger has occurred, but if we can understand the electromagnetic signatures from mergers well enough, perhaps we can search for candidate events even before we have a space-based gravitational wave observatory.”

The video below shows the expanding gravitational wave structure that would be expected to result from such a merger:

If ground-based telescopes can pinpoint the radio and x-ray flash created by the mergers, future space telescopes — like ESA’s eLISA/NGO — can then be used to try and detect the waves.

Read more on the NASA Goddard new release here.

First animation credit: NASA’s Goddard Space Flight Center/P. Cowperthwaite, Univ. of Maryland. Second animation: NASA/C. Henze.

 

Posted on by Nancy Atkinson

Students Discover Millisecond Pulsar, Help in the Search for Gravitational Waves

Using an array of millisecond pulsars, astronomers can detect tiny changes in the pulse arrival times in order to detect the influence of gravitational waves. Credit: NRAO

[/caption]

A special project to search for pulsars has bagged the first student discovery of a millisecond pulsar – a super-fast spinning star, and this one rotates about 324 times per second. The Pulsar Search Collaboratory (PSC) has students analyzing real data from the National Radio Astronomy Observatory’s (NRAO) Robert C. Byrd Green Bank Telescope (GBT) to find pulsars. Astronomers involved with the project said the discovery could help detect elusive ripples in spacetime known as gravitational waves.

“Gravitational waves are ripples in the fabric of spacetime predicted by Einstein’s theory of General Relativity,” said Dr. Maura McLaughlin, from West Virginia University. “We have very good proof for their existence but, despite Einstein’s prediction back in the early 1900s, they have never been detected.”

Four other pulsars have been discovered by high school students participating in this project.

Pulsar hunters Sydney Dydiw of Trinity High School, Emily Phan of George C. Marshall High School, Anne Agee of Roanoke Valley Governor's School, and Jessica Pal of Rowan County High School. Not pictured: Max Sterling of Langley High School. Credit: NRAO

“When you discover a pulsar, you feel like you’re walking on air! It is the best experience you can ever have,” said student co-discoverer Jessica Pal of Rowan County High School in Kentucky. “You get to meet astronomers and talk to them about your experience. I still can’t believe I found a pulsar. It is wonderful to know that there is something out there in space that you discovered.”

The other student involved in the discovery was Emily Phan of George C. Marshall High School in Virginia, who along with Pal found the millisecond pulsar on January 17, 2012. It was later confirmed by Max Sterling of Langley High School, Sydney Dydiw of Trinity High School, and Anne Agee of Roanoke Valley Governor’s School, all in Virginia.

“I am considering pursuing astronomy as a career choice,” said Agee. “The Pulsar Search Collaboratory has opened my eyes to how fun astronomy can be!”

Once the pulsar candidate was reported to NRAO, a followup observing session was scheduled on the giant, 17-million-pound telescope. On January 24, 2012, observations confirmed that the pulsar was real.

Pulsars are spinning neutron stars that sling “lighthouse beams” of radio waves around as they rotate. A neutron star is what is left after a massive star explodes at the end of its “normal” life. With no nuclear fuel left to produce energy to offset the stellar remnant’s weight, its material is compressed to extreme densities. The pressure squeezes together most of its protons and electrons to form neutrons; hence, the name “neutron star.” One tablespoon of material from a pulsar would weigh 10 million tons.

On January 24, 2012, observations with the Green Bank Telescope at 800 MHz confirmed that the signal was astronomical and zeroed in on its position. Pulsars are brighter at lower frequencies (like 350 MHz, above) than at higher frequencies, and so the confirmation plot is noisier than the original data. Since this pulsar spins so fast, it may be used as part of the pulsar timing array used to detect gravitational waves. Courtesy NRAO.

The object that the students discovered is a special class of pulsars called millisecond pulsars, which are the fastest-spinning neutron stars. They are highly stable and keep time more accurately than atomic clocks.

Astronomers don’t know much about them, however. But because of their stability, these pulsars may someday allow astronomers to detect gravitational waves.

Millisecond pulsars, however, could hold the key to that discovery. Like buoys bobbing on the ocean, pulsars can be perturbed by gravitational waves.

“Gravitational waves are invisible,” said McLaughlin. “But by timing pulsars distributed across the sky, we may be able to detect very small changes in pulse arrival times due to the influence of these waves.”

Millisecond pulsars are generally older pulsars that have been “spun up” by stealing mass from companion stars, but much is left to discover about their formation.

“This latest discovery will help us understand the genesis of millisecond pulsars,” said Dr. Duncan Lorimer, who is also part of the project. “It’s a very exciting time to be finding pulsars!”

Robert C. Byrd Green Bank Telescope CREDIT: NRAO/AUI/NSF

The PSC is a joint project of the National Radio Astronomy Observatory and West Virginia University, funded by a grant from the National Science Foundation. The PSC includes training for teachers and student leaders, and provides parcels of data from the GBT to student teams. The project involves teachers and students in helping astronomers analyze data from the GBT.

Approximately 300 hours of the observing data were reserved for analysis by student teams. These students have been working with about 500 other students across the country. The responsibility for the work, and for the discoveries, is theirs. They are trained by astronomers and by their teachers to distinguish between pulsars and noise.

The PSC will continue through the 2012-2013 school year. Teachers interested in participating in the program can learn more at this link. The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

Posted on by Tammy Plotner

LISA Pathfinder – Surfing Gravity Waves

LISA Pathfinder about to enter the space environment vacuum test. Credit: ESA

[/caption]

Do you remember the LISA mission? I do! The proposed launch for this unique vision is slated for 2014 and the latest sensor technology is making its own waves… by being far more accurate than expected. Now ESA’s LISA Pathfinder mission is better than ever, and ready to tackle the vast ocean of space in search of elusive gravitational waves…

So what’s new? By employing a near complete version of LISA, the Optical Meteorology Subsystem passed its first test under space-like temperature and vacuum conditions. Not only did it make the grade, but it went far beyond. It surpassed the precision requirement needed to detect gravitational waves by 300%!

Einstein predicted them, but to physically record this phenomenon in space, the LISA Pathfinder will utilize a laser to measure the distance between two free-floating gold–platinum cubes. Here on the ground, the team in Ottobrunn, Germany, are performing the tests using mirrors instead of cubes. Not only will the distance between them be cataloged, but their angles with respect to the laser beams. Is LISA good? Darn right. She had an accuracy rating of 10 billionths of a degree!

LISA Pathfinder with scientists in the clean room test environment. Credits: Astrium UK
“This is equivalent to the angle subtended by an astronaut’s footprint on the Moon!” notes Paul McNamara, Project Scientist for the LISA Pathfinder mission.

So how are gravitational waves detected? If perfect conditions do exist in space, then the free-floating cubes should mirror each other’s motions. Now, enter Einstein’s general theory of relativity. If some gravitational event should occur – such as the collision of two black holes – this should cause a minute distortion in the fabric of space. These tiny changes should be detectable. However, the accuracy needed to record such an event would need to be about one hundredth the size of an atom… a size called a “picometre”. Originally, LISA was optimized at 6 picometres measured over a timeline of 1000 seconds. But she bettered her record in 2010 and has now reached an amazing accuracy level of 2 picometres.

“The whole team has worked extremely hard to make this measurement possible,” said Dr McNamara. “When LISA Pathfinder is launched and we’re in the quiet environment of space some 1.5 million km from Earth, we expect that performance will be even better.”

Final preparation work on LISA Pathfinder ahead of the space environment testing. Credits: Astrium UK
The instrument team from Astrium GmbH, the Albert Einstein Institute and ESA are testing the Optical Metrology Subsystem during LISA Pathfinder thermal vacuum tests in Ottobrunn by spacecraft prime contractor Astrium (UK) Ltd. Tentatively set to launch in mid-2014, the LISA Pathfinder is well on its way to ride the gravitational waves and set the pace for ESA’s New Gravitational Wave Observatory. Perhaps within the next 10 years we’ll see even more advancements in finding the “final piece in Einstein’s cosmic puzzle.”

Way to go, LISA!

Original Story Source: ESA News Release.

Posted on by Tammy Plotner

Searching For Gravitational Waves

Two-dimensional representation of gravitational waves generated by two neutron stars surrounding each other. Credit: NASA

[/caption]Colliding neutron stars and black holes, supernova events, rotating neutron stars and other cataclysmic cosmic events… Einstein predicted they would all have something in common – oscillations in the fabric of space-time. This summer European scientists have joined forces to prove Einstein was right and capture evidence of the existence of gravitational waves.

Europe’s two ground-based gravitational wave detectors GEO600 (a German/UK collaboration) and Virgo (a collaboration between Italy, France, the Netherlands, Poland and Hungary) are underway with a joint observation program which will continue over the summer, ending in September 2011. The detectors consist of a pair of joined arms placed in a horizontal L-shaped configuration. Laser beams are then passed down the arms. Suspended under vacuum at the ends of the arms is a mirror which returns the beam to a central photodetector. The detectors work by measuring tiny changes (less than the diameter of a proton), caused by a passing gravitational wave, in the lengths (hundreds or thousands of meters). The periodic stretching and shrinking of the arms is then recorded as interference patterns.

Much like our human ears are able to distinguish the direction of sound from being spaced apart, so having interferometers placed at different locations benefits the chances of picking up a gravitational wave signal. By placing receivers at a distance, this also helps to eliminate the chances of picking up a mimicking terrestrial signal, since it would be unlikely for it to have the same characteristics at two locations while a genuine signal would remain the same.

“If you compare GEO600 and Virgo, you can see that both detectors have similar sensitivities at high frequencies, at around 600Hz and above”, says Dr Hartmut Grote, a scientist at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute/AEI) and the Leibniz University in Hannover, Germany. “That makes it very interesting for us to search this band for possible gravitational waves associated with supernovae or gamma-ray bursts that are observed with conventional telescopes.”

Of all phenomena, gamma-ray bursts are expected to be one of the strongest sources of gravitational waves. As the most luminous transient event in the known Universe, this collapse of a supermassive star core into a neutron star or black hole may be the most perfect starting point for the search. As of now, the frequencies will depend on the mass and may extend up to the kHz band. But don’t get too excited, because the nature of gravitational wave signals is weak and chances of picking up on it is low. However, thanks to Virgo’s excellent sensitivity at low frequencies (below 100 Hz), it is a prime candidate for gathering signals from isolated pulsars where the gravitational wave signal frequency should be at around 22Hz.

And we’ll be listening for the results…

Original Story Source: Albert Einstein Institute News.

Posted on by Ryan Anderson

New Pulsar “Clocks” Will Aid Gravitational Wave Detection

This illustration shows a pulsar’s magnetic field (blue) creates narrow beams of radiation (magenta). Image credit: NASA

How do you detect a ripple in space-time itself? Well, you need hundreds of precision clocks distributed throughout the galaxy, and the Fermi gamma ray telescope has given astronomers a new way to find them.

The “clocks” in question are actually millisecond pulsars – city-sized, sun-massed stars of ultradense matter that spin hundreds of times per second. Due to their powerful magnetic fields, pulsars emit most of their radiation in tightly focused beams, much like a lighthouse. Each spin of the pulsar corresponds to a “pulse” of radiation detectable from Earth. The rate at which millisecond pulsars pulse is extremely stable, so they serve as some of the most reliable clocks in the universe.

Astronomers watch for the slightest variations in the timing of millisecond pulsars which might suggest that space-time near the pulsar is being distorted by the passage of a gravitational wave. The problem is, to make a reliable measurement requires hundreds of pulsars, and until recently they have been extremely difficult to find.

“We’ve probably found far less than one percent of the millisecond pulsars in the Milky Way Galaxy,” said Scott Ransom of the National Radio Astronomy Observatory (NRAO).

Data from the Fermi gamma-ray space telescope, which started collecting data in 2008, have changed the way millisecond pulsars are detected. The Fermi telescope has identified hundreds of gamma-ray sources in the Milky Way. Gamma rays are high-energy photons, and they are produced near exotic objects, including millisecond pulsars.

“The data from Fermi were like a buried-treasure map,” Ransom said. “Using our radio telescopes to study the objects located by Fermi, we found 17 millisecond pulsars in three months. Large-scale searches had taken 10-15 years to find that many.”

Ransom and collaborator Mallory Roberts of Eureka Scientific used the National Science Foundation’s Robert C. Byrd Green Bank Telescope (GBT) to find eight of the 17 new pulsars.

Right now astronomers have only barely enough millisecond pulsars to make a convincing gravitational wave detection, but with Fermi to help identify more pulsars, the odds of detecting these ripples in space-time are steadily increasing.

Ransom and Roberts announced their discoveries today at the American Astronomical Society’s meeting in Washington, DC.

(NRAO Press Release)

Posted on by Nancy Atkinson

New Limits on Gravitational Waves From the Big Bang

Artists concept of graviational waves. Credit: NASA

[/caption]
The only way to know what the Universe was like at the moment of the Big Bang requires analysis of gravitational waves created when the Universe began. Scientists working with the Laser Interferometer Gravitational-Wave Observatory (LIGO) say their initial investigations of these gravitiation waves have turned up nothing. But that’s a good thing. Not detecting the waves provides constraints about the initial conditions of the universe, and narrows the field of where we actually do need to look in order to find them.

Much like it produced the cosmic microwave background, the Big Bang is believed to have created a flood of gravitational waves — ripples in the fabric of space and time. From our current understanding, gravitational waves are the only known form of information that can reach us undistorted from the beginnings of the Universe. They would be observed as a “stochastic” or random background, and would carry with them information about their violent origins and about the nature of gravity that cannot be obtained by conventional astronomical tools. The existence of the waves was predicted by Albert Einstein in 1916 in his general theory of relativity.

Analysis of data taken over a two-year period, from 2005 to 2007, yields that the stochastic background of gravitational waves has not yet been discovered. But the nondiscovery of the background, described in a new paper in the August 20 Nature, offers its own brand of insight into the universe’s earliest history.

“Since we have not observed the stochastic background, some of these early-universe models that predict a relatively large stochastic background have been ruled out,” said Vuk Mandic, assistant professor at the University of Minnesota and the head of the group that performed the analysis. “We now know a bit more about parameters that describe the evolution of the universe when it was less than one minute old.”

According to Mandic, the new findings constrains models of cosmic strings, objects that are proposed to have been left over from the beginning of the universe and subsequently stretched to enormous lengths by the universe’s expansion; the strings, some cosmologists say, can form loops that produce gravitational waves as they oscillate, decay, and eventually disappear.

“Since we have not observed the stochastic background, some of these early-universe models that predict a relatively large stochastic background have been ruled out,” said Mandic. “If cosmic strings or superstrings exist, their properties must conform with the measurements we made—that is, their properties, such as string tension, are more constrained than before.”

This is interesting, he says, “because such strings could also be so-called fundamental strings, appearing in string-theory models. So our measurement also offers a way of probing string-theory models, which is very rare today.”

The analysis used data collected from the LIGO interferometers in Hanford, Wash., and Livingston, La. Each of the L-shaped interferometers uses a laser split into two beams that travel back and forth down long interferometer arms. The two beams are used to monitor the difference between the two interferometer arm lengths.

The next phase of the project, called Advanced LIGO, will go online in 2014, and be 10 times more sensitive than the current instrument. It will allow scientists to detect cataclysmic events such as black-hole and neutron-star collisions at 10-times-greater distances.

The Nature paper is entitled “An Upper Limit on the Amplitude of Stochastic Gravitational-Wave Background of Cosmological Origin.”

Source: EurekAlert