Posted on by Jason Major

Effects of Einstein’s Elusive Gravitational Waves Observed

Chandra data (above, graph) on J0806 show that its X-rays vary with a period of 321.5 seconds, or slightly more than five minutes. This implies that the X-ray source is a binary star system where two white dwarf stars are orbiting each other (above, illustration) only 50,000 miles apart, making it one of the smallest known binary orbits in the Galaxy. According to Einstein's General Theory of Relativity, such a system should produce gravitational waves - ripples in space-time - that carry energy away from the system and cause the stars to move closer together. X-ray and optical observations indicate that the orbital period of this system is decreasing by 1.2 milliseconds every year, which means that the stars are moving closer at a rate of 2 feet per year.
Potential stellar collision. Credit: Chandra

Two white dwarfs similar to those in the system SDSS J065133.338+284423.37 spiral together in this illustration from NASA. Credit: D. Berry/NASA GSFC

Locked in a spiraling orbital embrace, the super-dense remains of two dead stars are giving astronomers the evidence needed to confirm one of Einstein’s predictions about the Universe.

A binary system located about 3,000 light-years away, SDSS J065133.338+284423.37 (J0651 for short) contains two white dwarfs orbiting each other rapidly — once every 12.75 minutes. The system was discovered in April 2011, and since then astronomers have had their eyes — and four separate telescopes in locations around the world — on it to see if gravitational effects first predicted by Einstein could be seen.

According to Einstein, space-time is a structure in itself, in which all cosmic objects — planets, stars, galaxies — reside. Every object with mass puts a “dent” in this structure in all dimensions; the more massive an object, the “deeper” the dent. Light energy travels in a straight line, but when it encounters these dents it can dip in and veer off-course, an effect we see from Earth as gravitational lensing.

Einstein also predicted that exceptionally massive, rapidly rotating objects — such as a white dwarf binary pair — would create outwardly-expanding ripples in space-time that would ultimately “steal” kinetic energy from the objects themselves. These gravitational waves would be very subtle, yet in theory, observable.

Read: Astronomy Without a Telescope: Gravitational Waves

What researchers led by a team at The University of Texas at Austin have found is optical evidence of gravitational waves slowing down the stars in J0651. Originally observed in 2011 eclipsing each other (as seen from Earth) once every six minutes, the stars now eclipse six seconds sooner. This equates to a predicted orbital period reduction of about 0.25 milliseconds each year.*

“These compact stars are orbiting each other so closely that we have been able to observe the usually negligible influence of gravitational waves using a relatively simple camera on a 75-year-old telescope in just 13 months,” said study lead author J.J. Hermes, a graduate student at The University of Texas at Austin.

Based on these measurements, by April 2013 the stars will be eclipsing each other 20 seconds sooner than first observed. Eventually they will merge together entirely.

Although this isn’t “direct” observation of gravitational waves, it is evidence inferred by their predicted effects… akin to watching a floating lantern in a dark pond at night moving up and down and deducing that there are waves present.

“It’s exciting to confirm predictions Einstein made nearly a century ago by watching two stars bobbing in the wake caused by their sheer mass,” said Hermes.

As of early last year NASA and ESA had a proposed mission called LISA (Laser Interferometer Space Antenna) that would have put a series of 3 detectors into space 5 million km apart, connected by lasers. This arrangement of precision-positioned spacecraft could have detected any passing gravitational waves in the local space-time neighborhood, making direct observation possible. Sadly this mission was canceled due to FY2012 budget cuts for NASA, but ESA is moving ahead with developments for its own gravitational wave mission, called eLISA/NGO — the first “pathfinder” portion of which is slated to launch in 2014.

The study was submitted to Astrophysical Journal Letters on August 24. Read more on the McDonald Observatory news release here.

Inset image: simulation of binary black holes causing gravitational waves – C. Reisswig, L. Rezzolla (AEI); Scientific visualization – M. Koppitz (AEI & Zuse Institute Berlin)

*The difference in the eclipse time is noted as six seconds even though the orbital period decay of the two stars is only .25 milliseconds/year because of a pile-up effect of all the eclipses observed since April 2011. The measurements made by the research team takes into consideration the phase change in the J0651 system, which experiences a piling effect — similar to an out-of-sync watch — that increases relative to time^2 and is therefore a larger and easier number to detect and work with. Once that was measured, the actual orbital period decay could be figured out.

Posted on by Jason Major

A New Species of Type Ia Supernova?

Artist’s conception of a binary star system that produces recurrent novae, and ultimately, the supernova PTF 11kx. (Credit: Romano Corradi and the Instituto de Astrofísica de Canarias)

Although they have been used as the “standard candles” of cosmic distance measurement for decades, Type Ia supernovae can result from different kinds of star systems, according to recent observations conducted by the Palomar Transient Factory team at California’s Berkeley Lab.


Judging distances across intergalactic space from here on Earth isn’t easy. Within the Milky Way — and even nearby galaxies — the light emitted by regularly pulsating stars (called Cepheid variables) can be used to determine how far away a region in space is. Outside of our own local group of galaxies, however, individual stars can’t be resolved, and so in order to figure out how far away distant galaxies are astronomers have learned to use the light from much brighter objects: Type Ia supernovae, which can flare up with a brilliance equivalent to 5 billion Suns.

Type Ia supernovae are created from a special pairing of two stars orbiting each other: one super-dense white dwarf drawing material in from a companion until a critical mass — about 40% more massive than the Sun — is reached. The overpacked white dwarf suddenly undergoes a rapid series of thermonuclear reactions, exploding in an incredibly bright outburst of material and energy… a beacon visible across the Universe.

Because the energy and luminance of Type Ia supernovae have been found to be so consistently alike, distance can be gauged by their apparent brightness as seen from Earth. The dimmer one is when observed, the farther away its galaxy is. Based on this seemingly universal similarity it’s been thought that these supernovae must be created under very similar situations… especially since none have been directly observed — until now.

An international team of astronomers working on the Palomar Transient Factory collaborative survey have observed for the first time a Type Ia supernova-creating star pair — called a progenitor system — located in the constellation Lynx. Named PTF 11kx, the system, estimated to be some 600 million light-years away, contains a white dwarf and a red giant star, a coupling that has not been seen in previous (although indirect) observations.

“It’s a total surprise to find that thermonuclear supernovae, which all seem so similar, come from different kinds of stars,” says Andy Howell, a staff scientist at the Las Cumbres Observatory Global Telescope Network (LCOGT) and a co-author on the paper, published in the August 24 issue of Science. “How could these events look so similar, if they had different origins?”

The initial observations of PTF 11kx were made possible by a robotic telescope mounted on the 48-inch Samuel Oschin Telescope at California’s Palomar Observatory as well as a high-speed data pipeline provided by the NSF, NASA and Department of Energy. The supernova was identified on January 16, 2011 and supported by subsequent spectrography data from Lick Observatory, followed up by immediate “emergency” observations with the Keck Telescope in Hawaii.

“We basically called up a fellow UC observer and interrupted their observations in order to get time critical spectra,” said Peter Nugent, a senior scientist at the Lawrence Berkeley National Laboratory and a co-author on the paper.

The Keck observations showed the PTF 11kx post-supernova system to contain slow-moving clouds of gas and dust that couldn’t have come from the recent supernova event. Instead, the clouds — which registered high in calcium in the Lick spectrographic data — must have come from a previous nova event in which the white dwarf briefly ignited and blew off an outer layer of its atmosphere. This expanding cloud was then seen to be slowing down, likely due to the stellar wind from a companion red giant.

(What’s the difference between a nova and a supernova? Read NASA’s STEREO Spots a New Nova)

Eventually the decelerating nova cloud was impacted by the rapidly-moving outburst from the supernova, evidenced by a sudden burst in the calcium signal which had gradually diminished in the two months since the January event. This calcium burst was, in effect, the supernova hitting the nova and causing it to “light up”.

The observations of PTF 11kx show that Type Ia supernova can occur in progenitor systems where the white dwarf has undergone nova eruptions, possibly repeatedly — a scenario that many astronomers had previously thought couldn’t happen. This could even mean that PTF 11kx is an entirely new species of Type Ia supernova, and while previously unseen and rare, not unique.

Which means our cosmic “standard candles” may need to get their wicks trimmed.

“We know that Type 1a supernovae vary slightly from galaxy to galaxy, and we’ve been calibrating for that, but this PTF 11kx observation is providing the first explanation of why this happens,” Nugent said. “This discovery gives us an opportunity to refine and improve the accuracy of our cosmic measurements.”

Source: Berkeley Lab news center

Inset images: PTF 11kx observation (BJ Fulton, Las Cumbres Observatory Global Telescope Network) / The 48-inch Samuel Oschin Telescope dome at Palomar Observatory. Video: Romano Corradi and the Instituto de Astrofísica de Canarias

Posted on by John Williams

Physicists Closing in on Understanding the Primordial Universe

Photo of the ALICE detector at CERN. Photo courtesy of CERN.

Slamming barely nothing together is bringing scientists ever-closer to understanding the weird states of matter present just milliseconds after the creation of the Universe in the Big Bang. This is according to physicists from CERN and Brookhaven National Laboratory, presenting their latest findings at the Quark Matter 2012 conference in Washington, DC.

By smashing ions of lead together within CERN’s lesser-known ALICE heavy-ion experiment, physicists said Monday that they created the hottest man-made temperatures ever. In an instant, CERN scientists recreated a quark-gluon plasma — at temperatures 38 percent hotter than a previous record 4-trillion degree plasma. This plasma is a subatomic soup and the very unique state of matter thought to have existed in the earliest moments after the Big Bang. Earlier experiments have shown these particular varieties of plasmas behave like perfect, frictionless liquids. This finding means that physicists are studying the densest and hottest matter ever created in a laboratory; 100,000 times hotter than the interior of our Sun and denser than a neutron star.

CERN’s scientists are just coming off of their July announcement of the discovery of the elusive Higgs boson.

“The field of heavy-ion physics is crucial for probing the properties of matter in the primordial universe, one of the key questions of fundamental physics that the LHC and its experiments are designed to address. It illustrates how in addition to the investigation of the recently discovered Higgs-like boson, physicists at the LHC are studying many other important phenomena in both proton–proton and lead–lead collisions,” said CERN Director-General Rolf Heuer.

According to a press release, the findings help scientists understand the “evolution of high-density, strongly interacting matter in both space and time.”

Meanwhile, scientists at Brookhaven’s Relativistic Heavy Ion Collider (RHIC), say they have observed the first glimpse of a possible boundary separating ordinary matter, composed of protons and neutrons, from the hot primordial plasma of quarks and gluons in the early Universe. Just as water exists in different phases, solid, liquid or vapor, depending on temperature and pressure, RHIC physicists are unraveling the boundary where ordinary matter starts to form from the quark gluon plasma by smashing gold ions together. Scientists are still not sure where to draw the boundary lines, but RHIC is providing the first clues.

The nuclei of today’s ordinary atoms and the primordial quark-gluon plasma, or QGP, represent two different phases of matter and interact at the most basic of Nature’s forces. These interactions are described in a theory known as quantum chromodynamics, or QCD. Findings from RHIC’s STAR and PHENIX show that the perfect liquid properties of the quark gluon plasma dominate at energies above 39 billion electron volts (GeV). As the energy dissipates, interactions between quarks and the protons and neutrons of ordinary matter begin to appear. Measuring these energies give scientists signposts pointing to the approach of a boundary between ordinary matter and the QGP.

“The critical endpoint, if it exists, occurs at a unique value of temperature and density beyond which QGP and ordinary matter can co-exist,” said Steven Vigdor, Brookhaven’s Associate Laboratory Director for Nuclear and Particle Physics, who leads the RHIC research program. “It is analogous to a critical point beyond which liquid water and water vapor can co-exist in thermal equilibrium, he said.

While Brookhaven’s particle accelerator cannot match CERN’s record-setting temperature conditions, scientists at the U.S Energy Department lab say the machine maps the “sweet spot” in this phase transition.

Image caption: The nuclear phase diagram: RHIC sits in the energy “sweet spot” for exploring the transition between ordinary matter made of hadrons and the early universe matter known as quark-gluon plasma. Courtesy of the U.S. Department of Energy’s Brookhaven National Laboratory.

John Williams is a science writer and owner of TerraZoom, a Colorado-based web development shop specializing in web mapping and online image zooms. He also writes the award-winning blog, StarryCritters, an interactive site devoted to looking at images from NASA’s Great Observatories and other sources in a different way. A former contributing editor for Final Frontier, his work has appeared in the Planetary Society Blog, Air & Space Smithsonian, Astronomy, Earth, MX Developer’s Journal, The Kansas City Star and many other newspapers and magazines.

Posted on by Jason Major

Winds of Change at the Edge of the Solar System

As the venerable Voyager 1 spacecraft hurtles ever outward, breaking through the very borders of our solar system at staggering speeds upwards of 35,000 mph, it’s sending back information about the curious region of space where the Sun’s outward flow of energetic particles meets the more intense cosmic radiation beyond — a boundary called the heliosheath.

Voyager 1 has been traveling through this region for the past seven years, all the while its instruments registering gradually increasing levels of cosmic ray particles. But recently the levels have been jumping up and down, indicating something new is going on… perhaps Voyager 1 is finally busting through the breakers of our Sun’s cosmic bay into the open ocean of interstellar space?

Data sent from Voyager 1 — a trip that currently takes the information nearly 17 hours to make — have shown steadily increasing levels of cosmic radiation as the spacecraft moves farther from the Sun. But on July 28, the levels of high-energy cosmic particles detected by Voyager jumped by 5 percent, with levels of lower-energy radiation from the Sun dropping by nearly half later the same day. Within three days both levels had returned to their previous states.

The last time such a jump in levels occurred was in May — and that spike took a week to happen.

“The increase and the decrease are sharper than we’ve seen before, but that’s also what we said about the May data,” said Edward Stone, the Voyager project scientist based at the California Institute of Technology. “The data are changing in ways that we didn’t expect, but Voyager has always surprised us with new discoveries.”

The graph below shows the jump in cosmic particles detected starting May 2012.

Over 11 billion miles (18 billion km) from home, Voyager 1 has been cruising through space since its launch on September 5, 1977. Its twin, Voyager 2, was launched two weeks earlier and is currently 9.3 billion miles (15 billion km) away. Both spacecraft are healthy and continue to communicate with Earth, and will both eventually break through the borders of our solar system and enter true interstellar space. If they are still operational when that happens — and there’s no reason that they shouldn’t be — we will finally get a sense of what conditions are like “out there”.

Although Voyager 1 is registering intriguing fluctuations in radiation from both inside and outside the Solar System, it’s not quite there yet.

“Our two veteran Voyager spacecraft are hale and healthy as they near the 35th anniversary of their launch,” said Suzanne Dodd, Voyager project manager based at JPL in Pasadena. “We know they will cross into interstellar space. It’s just a question of when.”

Read more about Voyager’s ongoing breakout here.

“We are certainly in a new region at the edge of the solar system where things are changing rapidly. But we are not yet able to say that Voyager 1 has entered interstellar space.”

–  Edward Stone, Voyager project scientist, Caltech

Images: NASA/JPL-Caltech

Posted on by John Williams

A Crinkle in the Wrinkle of Space-time

Albert Einstein’s revolutionary general theory of relativity describes gravity as a curvature in the fabric of spacetime. Mathematicians at University of California, Davis have come up with a new way to crinkle that fabric while pondering shockwaves.

“We show that spacetime cannot be locally flat at a point where two shockwaves collide,” says Blake Temple, professor of mathematics at UC Davis. “This is a new kind of singularity in general relativity.”

Temple and his collaborators study the mathematics of how shockwaves in a perfect fluid affect the curvature of spacetime. Their new models prove that singularities appear at the points where shock waves collide. Vogler’s mathematical models simulated two shockwaves colliding. Reintjes followed up with an analysis of the equations that describe what happens when the shockwaves cross. He dubbed the singularity created a “regularity singularity.”

“What is surprising,” Temple told Universe Today, “is that something as mundane as the interaction of waves could cause something as extreme as a spacetime singularity — albeit a very mild new kind of singularity. Also surprising is that they form in the most fundamental equations of Einstein’s theory of general relativity, the equations for a perfect fluid.”

The results are reported in two papers by Temple with graduate students Moritz Reintjes and Zeke Vogler in the journal Proceedings of the Royal Society A.

Einstein revolutionized modern physics with his general theory of relativity published in 1916. The theory in short describes space as a four-dimensional fabric that can be warped by energy and the flow of energy. Gravity shows itself as a curvature of this fabric. “The theory begins with the assumption that spacetime (a 4-dimensional surface, not 2 dimensional like a sphere), is also “locally flat,” Temple explains. “Reintjes’ theorem proves that at the point of shockwave interaction, it [spacetime] is too “crinkled” to be locally flat.”

We commonly think of a black hole as being a singularity which it is. But this is only part of the explanation. Inside a black hole, the curvature of spacetime becomes so steep and extreme that no energy, not even light, can escape. Temple says that a singularity can be more subtle where just a patch of spacetime cannot be made to look locally flat in any coordinate system.

“Locally flat” refers to space that appears to be flat from a certain perspective. Our view of the Earth from the surface is a good example. Earth looks flat to a sailor in the middle of the ocean. It’s only when we move far from the surface that the curvature of the Earth becomes apparent. Einstein’s theory of general relativity begins with the assumption that spacetime is also locally flat. Shockwaves create an abrupt change, or discontinuity, in the pressure and density of a fluid. This creates a jump in the curvature of spacetime but not enough to create the “crinkling” seen in the team’s models, Temple says.

The coolest part of the finding for Temple is that everything, his earlier work on shockwaves during the Big Bang and the combination of Vogler’s and Reintjes’ work, fits together.

There is so much serendipity,” says Temple. “This is really the coolest part to me.
I like that it is so subtle. And I like that the mathematical field of shockwave theory, created to address problems that had nothing to do with General Relativity, has led us to the discovery of a new kind of spacetime singularity. I think this is a very rare thing, and I’d call it a once in a generation discovery.”

While the model looks good on paper, Temple and his team wonder how the steep gradients in spacetime at a “regularity singularity” could cause larger than expected effects in the real world. General relativity predicts gravity waves might be produced by the collision of massive objects, such as black holes. “We wonder whether an exploding stellar shock wave hitting an imploding shock at the leading edge of a collapse, might stimulate stronger than expected gravity waves,” Temple says. “This cannot happen in spherical symmetry, which our theorem assumes, but in principle it could happen if the symmetry were slightly broken.”

Image caption: Artist rendition of the unfurling of spacetime at the beginning of the Big Bang. John Williams/TerraZoom

Posted on by Nancy Atkinson

Passing Through – A Beautiful Iceland Timelapse

This awesome video by Kristian Ulrich Larsen and Olafur Haraldsson melds the stark but beautiful landscape of Iceland, the words of Nicola Tesla, and cool computer graphics.

The text is from a speech given by Tesla in 1893, where he implies that the world should be conceived as a whole where everything is interconnected.

“Like a wave in the physical world, in the infinite ocean of the medium which pervades all, so in the world of organisms, in life, an impulse started proceeds onward, at times, may be, with the speed of light, at times, again, so slowly that for ages and ages it seems to stay, passing through processes of a complexity inconceivable to men, but in all its forms, in all its stages, its energy ever and ever integrally present.

A single ray of light from a distant star falling upon the eye of a tyrant in bygone times may have altered the course of his life, may have changed the destiny of nations, may have transformed the surface of the globe, so intricate, so inconceivably complex are the processes in Nature. In no way can we get such an overwhelming idea of the grandeur of Nature than when we consider, that in accordance with the law of the conservation of energy, throughout the Infinite, the forces are in a perfect balance, and hence the energy of a single thought may determine the motion of a universe.”

—Nikola Tesla “The Electrical Review, 1893”

Passing Through from Olafur Haraldsson on Vimeo.

Posted on by John Williams

Hubble Spies Tiny, Ancient ‘Ghost Galaxies’

These Hubble images show the dim, star-starved dwarf galaxy Leo IV. The image at left shows part of the galaxy, outlined by the white rectangular box. The box measures 83 light-years wide by 163 light-years long. The few stars in Leo IV are lost amid neighboring stars and distant galaxies. A close-up view of the background galaxies within the box is shown in the middle image. The image at right shows only the stars in Leo IV. The galaxy, which contains several thousand stars, is composed of sun-like stars, fainter, red dwarf stars, and some red giant stars brighter than the sun. Credit: NASA, ESA, and T. Brown (STScI)

They’re out there; tiny, extremely faint and incredibly ancient dwarf galaxies with so few stars that scientists call them ‘ghost galaxies.’ NASA’s Hubble Space Telescope captured images of three of these small-fry galaxies in hopes of unraveling a mystery 13 billion years in the making.

Astronomers believe these tiny, ghost-like galaxies spotted alongside the Milky Way Galaxy are among the oldest, tiniest and most pristine galaxies in the Universe. Hubble views reveal that their stars share the same birth date. The galaxies all started forming stars more than 13 billions years ago but then abruptly stopped within just one billion years after the Universe was born.

“These galaxies are all ancient and they’re all the same age, so you know something came down like a guillotine and turned off the star formation at the same time in these galaxies,” said Tom Brown of the Space Telescope Science Institute in Baltimore, Md., the study’s leader. “The most likely explanation is reionization.”

Reionization of the Universe began in the first billion years after the Big Bang. During this time, radiation from the first stars knocked electrons off hydrogen atoms, ionizing the hydrogen gas. This process also allowed hydrogen gas to become transparent to ultraviolet light. This same process may also have squashed star-making in dwarf galaxies, such as those in Brown’s study. These galaxies are tiny cousins to star-making dwarf galaxies near the Milky Way. And because of their small size, just 2,000 light-years across, they were not massive enough to shield themselves from the harsh ultraviolet light of the early Universe which stripped away their meager supply of hydrogen gas, leaving them unable to make new stars.

Astronomers proposed many reasons for the lack of stars in these galaxies in addition to the reioniation theory. Some scientists believed internal events such as supernovae blasted away the gas needed to create new stars. Others suggested that the galaxies simply used up their supply of hydrogen gas needed to make stars.

Brown measured the stars’ ages by looking at their brightness and colors. The stellar populations in these fossil galaxies range from a few hundred to a few thousand stars; some sun-like, some red dwarfs and some red stars larger than our Sun. When evidence showed that the stars were indeed ancient, Brown enlisted the help of Hubble’s Advanced Camera for Surveys to burrow deep within six galaxies to determine when they were born. So far, the team has finished analyzing data for three; Hercules, Leo IV and Ursa Major. The galaxies lie between 330,000 light-years to 490,000 light-years. For comparison, Brown compared the galaxies’ stars with those found in M92, a 13 billion-year-old globular cluster located about 26,000 light-years from Earth. He found they are of similar age.

“These are the fossils of the earliest galaxies in the universe,” Brown said. “They haven’t changed in billions of years. These galaxies are unlike most nearby galaxies, which have long star-formation histories.”

Brown’s discovery could help explain the so-called “missing satellite problem.” Astronomers have observed only a few dozen dwarf galaxies around the Milky Way while computer simulations predict thousands should exist. But perhaps they do exist. The Sloan survey found more than a dozen tiny, star-starved galaxies in the Milky Way’s neighborhood while scanning just a portion of the sky. Astronomers think that dozens more ultra-faint galaxies may lurk undetected with the possibility of thousands of even smaller dwarfs containing virtually no stars.

The tiny galaxies may be star-deprived but they still have an abundance of dark matter, the framework upon which galaxies are built. Normal dwarf galaxies near the Milky Way Galaxy contain ten times more dark matter than ordinary visible matter. Brown explains that these tiny galaxies are now islands of mostly dark matter, unseen for billions of years until astronomers began finding them in the Sloan Survey.

Brown’s results appear in the July 1 issue of the Astrophysical Journal Letters.

Image caption 1: These Hubble images show the dim, star-starved dwarf galaxy Leo IV. The image at left shows part of the galaxy, outlined by the white rectangular box. The box measures 83 light-years wide by 163 light-years long. The few stars in Leo IV are lost amid neighboring stars and distant galaxies. A close-up view of the background galaxies within the box is shown in the middle image. The image at right shows only the stars in Leo IV. The galaxy, which contains several thousand stars, is composed of sun-like stars, fainter, red dwarf stars, and some red giant stars brighter than the sun. Credit: NASA, ESA, and T. Brown (STScI)

Image caption 2: These computer simulations show a swarm of dark matter clumps around our Milky Way galaxy. Some of the dark-matter concentrations are massive enough to spark star formation. Thousands of clumps of dark matter coexist with our Milky Way galaxy, shown in the center of the top panel. The green blobs in the middle panel are those dark-matter chunks massive enough to obtain gas from the intergalactic medium and trigger ongoing star formation, eventually creating dwarf galaxies. In the bottom panel, the red blobs are ultra-faint dwarf galaxies that stopped forming stars long ago. Credit: NASA, ESA, and T. Brown and J. Tumlinson (STScI)

Posted on by Nancy Atkinson

Dark Galaxies Found from the Early Universe

Caption: This deep image shows the region of the sky around the quasar HE0109-3518, near the center of the image. The energetic radiation of the quasar makes dark galaxies glow, helping astronomers to understand the obscure early stages of galaxy formation. Credit:ESO, Digitized Sky Survey 2 and S. Cantalupo (UCSC)


How do you find a dark galaxy? Shine some light on the subject. Dark galaxies — ancient galaxies that contain little to no stars — have been theorized to exist but have not been observed, until now. An international team of astronomers think they have detected these elusive objects by observing them glowing as they are illuminated by a quasar.

Dark galaxies are small, gas-rich galaxies in the early Universe that are very inefficient at forming stars. They are predicted by theories of galaxy formation and are thought to be the building blocks of today’s bright, star-filled galaxies. Astronomers think that they may have fed large galaxies with much of the gas that later formed into the stars that exist today.

Being essentially devoid of stars, these dark galaxies don’t emit much light, making them very hard to detect. For years astronomers have been trying to develop new techniques that could confirm the existence of these galaxies. Small absorption dips in the spectra of background sources of light have hinted at their existence. However, this new study marks the first time that such objects have been seen directly.

“Our approach to the problem of detecting a dark galaxy was simply to shine a bright light on it,” said Simon Lilly, from the Institute for Astronomy at ETH Zurich, Switzerland) co-author of a new paper published in the Monthly Notices of the Royal Astronomical Society. “We searched for the fluorescent glow of the gas in dark galaxies when they are illuminated by the ultraviolet light from a nearby and very bright quasar. The light from the quasar makes the dark galaxies light up in a process similar to how white clothes are illuminated by ultraviolet lamps in a night club.”

Fluorescence is the emission of light by a substance illuminated by a light source. Quasars are very bright, distant galaxies, and their brightness makes them powerful beacons that can help to illuminate the surrounding area, probing the era when the first stars and galaxies were forming out of primordial gas.

This video zooms into the region around the quasar, HE 0109-3518:

In order to detect the extremely faint fluorescent glow of these dark galaxies, the team used the Very Large Telescope (VLT), and took a series of very long exposures, mapping a region of the sky around the bright quasar HE 0109-3518. They looked for the ultraviolet light that is emitted by hydrogen gas when it is subjected to intense radiation.

The team detected almost 100 gaseous objects lying within a few million light-years of the quasar, and narrowed the possible dark galaxies down to 12 objects. The team says these are the most convincing identifications of dark galaxies in the early Universe to date.

“Our observations with the VLT have provided evidence for the existence of compact and isolated dark clouds,” said Sebastiano Cantalupo from the University of California, Santa Cruz, lead author of the paper. “With this study, we’ve made a crucial step towards revealing and understanding the obscure early stages of galaxy formation and how galaxies acquired their gas.”

The astronomers were also able to determine some of the properties of the dark galaxies, and estimate that the mass of the gas in them is about 1 billion times that of the Sun, typical for gas-rich, low-mass galaxies in the early Universe. They were also able to estimate that the star formation efficiency is suppressed by a factor of more than 100 relative to typical star-forming galaxies found at similar stage in cosmic history.

Read the team’s paper.

Source: ESO

Posted on by John Williams

Life and Death in a Tangled Web of Space

The Vela-C molecular cloud region as observed in far-infrared wavelengths. Credit: CNRS/INSU - Univ. Paris Diderot, France

In a star-making nebula awash in a tangled nest of gas and glowing filaments, scientists have uncovered an interesting, previously unseen interplay between gravity and turbulence that affects the formation of stars.

This image, taken by the European Space Agency’s Herschel Space Observatory, shows the highly detailed structure of cool wispy filaments of the Vela C molecular cloud. Located just 2,300 light-years from Earth, Vela-C is a vast star-making complex of gas and dust. And within this glowing cloud, both high-mass stars and smaller Sun-like stars form through very different processes.

Gravitational attraction pulls gas and dust together to form massive clumps of matter in glowing ridges. According to scientists studying the image, the most massive and brightest stars will form within these clumps. Random motion and turbulence throughout the cloud appear to create the fine nest-like filaments. It’s within these areas that smaller stars will form. Tiny, white specks fleck the image. These white dots, more abundant in the ridge-like filaments, are pre-stellar cores; compact clumps of gas and dust that might ignite into new stars.

Vela-C’s proximity to Earth makes it an ideal laboratory to study the birth of different kinds of stars. The nebula may also make it a perfect study of supernovae. The blue areas in the image contain expanding pockets of hot gas energized by the strong solar wind and ultraviolet radiation of young and massive stars. Compared to our Sun’s expected 10 billion year life-span, these massive stars burn through their supply of nuclear fuel within just a few million years. At the end of their lives, these stars will explode in dazzling supernovae.

The Herschel Telescope, launched in 2009, explores the Universe in the far infrared. While interstellar dust is cold, it shines brightly against the even colder surrounding space. The longest wavelengths of light show up as the red filaments in this image. Shorter, signifying hotter, wavelengths of light show up as yellow, green and blue.

Image Caption: The Vela-C molecular cloud region observed in far-infrared wavelengths. Credit: ESA/PACS/SPIRE/Tracey Hill & Frédérique Motte, Laboratoire AIM Paris-Saclay, CEA/Irfu – CNRS/INSU – Univ. Paris Diderot, France

Posted on by John Williams

Galactic Gong – Milky Way Struck and Still Ringing After 100 Million Years

Small Magellanic Cloud
Small Magellanic Cloud

When galaxies collide, stars are thrown from orbits, spiral arms are stretched and twisted, and now scientists say galaxies ring like a bell long after the cosmic crash.

A team of astronomers from the United States and Canada say they have heard echoes of that ringing, possible evidence of a galactic encounter 100 million years ago when a small satellite galaxy or dark matter object passed through the Milky Way Galaxy; close to our position in the galaxy, as if a rock were thrown into a still pond causing the stars to bounce up and down on the waves. Their results were published in the Astrophysical Journal Letters.

“We have found evidence that our Milky Way had an encounter with a small galaxy or massive dark matter structure perhaps as recently as 100 million years ago,” said Larry Widrow, professor at Queen’s University in Canada. “We clearly observe unexpected differences in the Milky Way’s stellar distribution above and below the Galaxy’s midplane that have the appearance of a vertical wave — something that nobody has seen before.”

Astronomers took observations from about 300,000 nearby stars in the Sloan Digital Sky Survey. Stars move up and down at 20-30 kilometers per second while see-sawing around the galaxy at 220 kilometers per second. By comparison, the International Space Station putters around Earth at 7.71 kilometers per second; Voyager 1, the fastest man-made object, currently is leaving the solar system at about 17.46 kilometers per second. Widrow and colleagues at the University of Kentucky, The University of Chicago and Fermi National Accelerator Laboratory found that the positions of nearby stars is not quite as regular as previously thought. The team noticed a small but statistically significant difference in the distribution of stars above and below the midplane of the Milky Way.

“Our part of the Milky Way is ringing like a bell,” said Brian Yanny, of the Department of Energy’s Fermilab. “But we have not been able to identify the celestial object that passed through the Milky Way. It could have been one of the small satellite galaxies that move around the center of our galaxy, or an invisible structure such as a dark matter halo.”

Susan Gardner, professor of physics at the University of Kentucky added, “The perturbation need not have been a single isolated event in the past, and it may even be ongoing. Additional observations may well clarify its origin.”

Other possibilities considered for the variations were the effect of interstellar dust or simply the way the stars were selected in the survey. But as those events failed to explain fully the observations, the astronomers began to explore possible recent events in the history of the galaxy.

More than 20 visible satellite galaxies circle the Milky Way. Invisible satellites made up of dark matter, hypothetical matter that cannot be seen but is thought to make up a majority of the mass of the Universe, might also orbit our galaxy. Scientists believe that most of the mass orbiting the galaxy is in the form of dark matter. Using computer simulations to explore the effects of a small galaxy or dark matter structure passing through the disk of the Milky Way, the scientists developed a clearer picture of the see-saw effects they were seeing.

In terms of the nine-billion lifetime of the Milky Way Galaxy, the effects are short-lived. This part of the galaxy has been “ringing” for 100 million years and will continue for 100 million years more as the up-and-down motion dissipates, say the astronomers – unless we are hit again.

Image caption: The Small Magellanic Cloud is one of 20 visible satellite galaxies that orbit the Milky Way Galaxy. Astronomers report that a smaller counterpart or dark matter object passed through the Milky Way near our position about 100 million years ago.