Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Cosmic Slurp


Georgia Tech researchers use XSEDE supercomputers to understand and predict how black holes swallow stars

Somewhere in the cosmos an ordinary galaxy spins, seemingly at slumber. Then all of a sudden, WHAM! A flash of light explodes from the galaxy's center. A star orbiting too close to the event horizon of the galaxy's central supermassive black hole is torn apart by the force of gravity, heating up its gas and sending out a beacon to the far reaches of the universe.

Black Hole Caught Red-handed in a Stellar Homicide. [Credit: NASA; S. Gezari (The Johns Hopkins University); and J. Guillochon (University of California, Santa Cruz)]

In a universe with tens of billions of galaxies, how would we see it? What would such a beacon look like? How would we distinguish it from other bright, monumental intergalactic events, like supernovas?

"Black holes by themselves do not emit light," said Tamara Bogdanovic, Assistant Professor of Physics at the Georgia Institute of Technology. "Our best chance to discover them in distant galaxies is if they interact with stars and gas that are around them."

In recent decades, with improved telescopes and observational techniques designed to repeatedly survey the vast numbers of galaxies on the sky, scientists noticed that some galaxies that previously looked inactive would suddenly light up at their very center.

"This flare of light was found to have a characteristic behavior as a function of time," Bogdanovic explained. "It starts very bright and its luminosity then decreases in time in a particular way. Astronomers have identified those as galaxies where a central black hole just disrupted and ‘ate' a star. It's like a black hole putting up a sign that says: ‘Here I am.'"

Bogdanovic relies on National Science Foundation-funded supercomputers like Stampede at the Texas Advanced Computing Center and Kraken at the National Institute for Computational Sciences. Using these systems, she and her collaborators recently simulated the dynamics of these super powerful forces and charted their behavior using numerical models. Stampede and Kraken are part of the Extreme Science and Engineering Discovery Environment (XSEDE), a single virtual system that scientists use to interactively share computing resources, data and expertise.

Using a mix of theoretical and computational approaches, Bogdanovic tries to predict the observational signatures of events like the black-hole-devouring-star scenario described above, also known as a "tidal disruption"— or two supermassive black holes merging, another of her interests. Such events would have a distinct signature to someone analyzing data from a ground-based or a space-based observatory.

Tidal disruptions are rare cosmic occurrences.

Astrophysicists have calculated that a Milky Way-like galaxy stages the disruption of a star only once in about 10,000 years. The luminous flare of light, on the other hand, can fade away in only a few years. This difference in timescale highlights the observational challenge in pinpointing such events in the sky and underlines the importance of astronomical surveys that monitor vast numbers of galaxies at the same time.

So far, only a few dozen of these characteristic flare signatures have been observed and deemed "candidates" for tidal disruptions. But with data from PanSTARRS, Galex, the Palomar Transient Factory and other upcoming astronomical surveys becoming available to scientists, Bogdanovic believes this scarcity will change dramatically.

"As opposed to a few dozen that have been found over the past 10 years, now imagine hundreds per year — that's a huge difference!" she said. "It means that we will be able to build a varied sample of stars of different types being disrupted by supermassive black holes."

With hundreds of such events to explore, astrophysicists' understanding of black holes and the stars around them would advance by leaps and bounds, helping determine some key aspects of galactic physics.

"A diversity in the type of disrupted stars tells us something about the makeup of the star clusters in the centers of galaxies," Bodganovic said. "It may give us an idea about how many main sequence stars, how many red giants, or white dwarf stars are there on average."

It also tells us something about the population and properties of supermassive black holes that are doing the disrupting.

"We use these observations as a window of opportunity to learn important things about the black holes and their host galaxies," she continued. "Once the tidal disruption flare dims below some threshold luminosity that can be seen in observations, the window closes for that particular galaxy."

In a recent paper submitted to the Astrophysical Journal, Bogdanovic, working with Roseanne Cheng (Center for Relativistic Astrophysics at Georgia Tech) and Pau Amaro-Seoane (Albert Einstein Institute in Potsdam, Germany), considered the tidal disruption of a red giant star by a supermassive black hole using computer modeling.

The paper comes on the heels of the discovery of a tidal disruption event in which a black hole disrupted a helium-rich stellar core, thought to be a remnant of a red giant star, named PS1-10jh, 2.7 billion light years from Earth.

The sequence of events they described aims to explain some unusual aspects of the observational signatures associated with this event, such as the absence of the hydrogen emission lines from the spectrum of PS1-10jh.

As a follow-up to this theoretical study, the team has been running simulations on Georgia Tech's Keeneland supercomputer, in addition to as Stampede and Kraken. The simulations reconstruct the chain of events by which a stellar core, similar to the remnant of a tidally disrupted red giant star, might evolve under the gravitational tides of a massive black hole.

"Calculating the messy interplay between hydrodynamics and gravity is feasible on a human timescale only with a supercomputer," Cheng said. "Because we have control over this virtual experiment and can repeat it, fast forward, or rewind as needed, we can examine the tidal disruption process from many perspectives. This in turn allows us to determine and quantify the most important physical processes at play."

The research shows how computer simulations complement and constrain theory and observation.

"There are many situations in astrophysics where we cannot get insight into a sequence of events that played out without simulations," Bogdanovic said. "We cannot stand next to the black hole and look at how it accretes gas. So we use simulations to learn about these distant and extreme environments."

One of Bogdanovic's goals is to use the knowledge gained from simulations to decode the signatures of observed tidal disruption events.

"The most recent data on tidal disruption events is already outpacing theoretical understanding and calling for the development of a new generation of models," she explained. "The new, better quality data indicates that there is a great diversity among the tidal disruption candidates. This is contrary to our perception, based on earlier epochs of observation, that they are a relatively uniform class of events. We are yet to understand what causes these differences in observational appearance and computer simulations are guaranteed to be an important part of this journey."

Faith Singer | Eurek Alert!
Further information:

Further reports about: Cosmic Kraken black hole computer simulations diversity gravity observations sequence telescopes

More articles from Physics and Astronomy:

nachricht Stellar desk in wave-like motion
08.10.2015 | Max Planck Institute for Astronomy, Heidelberg

nachricht Mysterious ripples found racing through planet-forming disk
08.10.2015 | NASA/Goddard Space Flight Center

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Reliable in-line inspections of high-strength automotive body parts within seconds

Nondestructive material testing (NDT) is a fast and effective way to analyze the quality of a product during the manufacturing process. Because defective materials can lead to malfunctioning finished products, NDT is an essential quality assurance measure, especially in the manufacture of safety-critical components such as automotive B-pillars. NDT examines the quality without damaging the component or modifying the surface of the material. At this year's Blechexpo trade fair in Stuttgart, Fraunhofer IZFP will have an exhibit that demonstrates the nondestructive testing of high-strength automotive body parts using 3MA. The measurement results are available in a matter of seconds.

To minimize vehicle weight and fuel consumption while providing the highest level of crash safety, automotive bodies are reinforced with elements made from...

Im Focus: Kick-off for a new era of precision astronomy

The MICADO camera, a first light instrument for the European Extremely Large Telescope (E-ELT), has entered a new phase in the project: by agreeing to a Memorandum of Understanding, the partners in Germany, France, the Netherlands, Austria, and Italy, have all confirmed their participation. Following this milestone, the project's transition into its preliminary design phase was approved at a kick-off meeting held in Vienna. Two weeks earlier, on September 18, the consortium and the European Southern Observatory (ESO), which is building the telescope, have signed the corresponding collaboration agreement.

As the first dedicated camera for the E-ELT, MICADO will equip the giant telescope with a capability for diffraction-limited imaging at near-infrared...

Im Focus: Locusts at the wheel: University of Graz investigates collision detector inspired by insect eyes

Self-driving cars will be on our streets in the foreseeable future. In Graz, research is currently dedicated to an innovative driver assistance system that takes over control if there is a danger of collision. It was nature that inspired Dr Manfred Hartbauer from the Institute of Zoology at the University of Graz: in dangerous traffic situations, migratory locusts react around ten times faster than humans. Working together with an interdisciplinary team, Hartbauer is investigating an affordable collision detector that is equipped with artificial locust eyes and can recognise potential crashes in time, during both day and night.

Inspired by insects

Im Focus: Physicists shrink particle accelerator

Prototype demonstrates feasibility of building terahertz accelerators

An interdisciplinary team of researchers has built the first prototype of a miniature particle accelerator that uses terahertz radiation instead of radio...

Im Focus: Simple detection of magnetic skyrmions

New physical effect: researchers discover a change of electrical resistance in magnetic whirls

At present, tiny magnetic whirls – so called skyrmions – are discussed as promising candidates for bits in future robust and compact data storage devices. At...

All Focus news of the innovation-report >>>



Event News

EHFG 2015: Securing healthcare and sustainably strengthening healthcare systems

01.10.2015 | Event News

Conference in Brussels: Tracking and Tracing the Smallest Marine Life Forms

30.09.2015 | Event News

World Alzheimer`s Day – Professor Willnow: Clearer Insights into the Development of the Disease

17.09.2015 | Event News

Latest News

Unexpected information about Earth's climate history from Yellow River sediment

09.10.2015 | Earth Sciences

Single atom alloy platinum-copper catalysts cut costs, boost green technology

09.10.2015 | Life Sciences

Indefatigable Hearing

09.10.2015 | Life Sciences

More VideoLinks >>>