Category Archives: Astronomy

Giant halos discovered around early Milky-Way galaxies

Astronomers have looked 11 billion years into the past to discover giant halos around early Milky-Way galaxies.

The discovery was made by astronomers led by David Sobral from Lancaster University in the UK and Jorryt Matthee from Leiden University in the Netherlands. The team reports its findings in the journal Monthly Notices of the Royal Astronomical Society.

Artistic impression showing a Milky-Way type galaxy surrounded by a halo of light around 100 thousand light-years across. Image credit: ESO/L.Calçada.

In order to understand how our own Milky Way galaxy formed and evolved, astronomers rely on observing distant galaxies.

As their light takes billions of years to reach us, telescopes can be used as time machines, as long as we have a clear time-travelling indicator to pin-point the distance.

However, when we travel more than 11 billion years into the past, there is only one major feature which telescopes can identify: Lyman-alpha photons.

Jorryt Matthee comments: “Newly born stars in very distant galaxies break apart hydrogen in surrounding clouds of gas, which then shines brightly in Lyman-α light, in theory the strongest of such features observable in a distant galaxy. Yet, in practice, Lyα photons struggle to escape galaxies as gas and dust block and diverge their travel paths, making it a complex process to understand.”

Astronomers developed a unique experiment using the Isaac Newton Telescope (INT) in La Palma to look at almost 1000 very distant galaxies in a stereoscopic way. They surveyed the sky using the Wide Field Camera (WFC) and custom-made filters in order to measure where Lyα is produced, how much, and where it comes out of galaxies.

Dr David Sobral says “We have used dozens of dedicated nights on the INT with our own narrow-band filter in order to understand how Lyα photons escape from distant galaxies. We have looked back in time 11 billion years, essentially the limit where we can still use multiple features to identify distant galaxies and study them in detail. We were able to predict how many Lyα photons were effectively produced in each distant galaxy and where this happened. Then we compared them with the ones that actually reach the INT.”

The results show that while these photons are so used to study the very early Universe, only 1-2% of those photons escape from the centres of galaxies like the Milky way. Even if we account for all the photons at a large distance from the center, less than 10% escape.

Dr Sobral said: “In other words, all galaxies forming stars in the distant Universe seem to be surrounded by an impressively large, faint halo of Lyα photons that had to travel for hundreds of thousands of light years in an almost endless series of absorption and re-emission events, until they were finally free. We now need to understand exactly how and why that happens.”

Astronomers expect that the James Webb Space Telescope will be able to extend these studies to even higher look-back times, opening up a new window into the study of galaxy formation and evolution. Studying how the escape fraction evolves with redshift can tell us about the kind of stars producing Lyα photons, and the properties of interstellar and intergalactic gas.

Source: Lancaster University

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What role do supermassive black holes play when galaxies merge?

In roughly four billion years, the Milky Way will be no more.

Indeed, our home galaxy is on course to collide and unite with the Andromeda Galaxy, at present some two million light years away.

This image shows three instances of merging galaxies located at least a billion light years from Earth. Each galaxy is as large as the Milky Way and contains about 100 billion stars. Violent gravitational interactions created the tidal tails shown and triggered massive black hole accretion at the galactic nuclei. These systems were first confirmed by Hai Fu in 2015 and published in “Astrophysical Journal Letters.” Image credit: Hai Fu.

Of course, we don’t notice that the two galaxies are drawing closer together.

“To the human perspective, our galaxy doesn’t appear to be changing,” says University of Iowa astrophysicist Hai Fu, “but in the history of the universe, it is changing all the time.”

Galaxies have been merging for most of the universe’s 13-billion-year history, and scientists have been observing these mergers for some time. What they don’t fully understand is how mergers occur.

Fu, an assistant professor in physics and astronomy, aims to clarify the phenomenon by observing supermassive black holes (with a mass of about one billion suns), which are at the center of most galaxies. Astrophysicists believe large galaxies grow by devouring smaller ones. In such cases, the black holes of both are expected to orbit each other and eventually merge. Fu and his team won a three-year, $405,011 grant from the National Science Foundation to find and characterize these celestial events.

“What we’re trying to see is the late stages of merging galaxies, when two galaxies are so close together they unleash tidal forces of energy, kind of like the pulsing tidal forces caused when the sun and moon line up with the Earth but much, much more intense,” he says.

Fu will scan a large chunk of the night sky—imagine the moon multiplied 1,200 across the sky and you’ll have a sense of the size—to find evidence of black holes’ accretion, or mass-gathering.

“Pairs of galaxies with accreting black holes are rare and difficult to find,” Fu says, “and that’s why we need such a large area to survey.”

Black holes aren’t always accreting. But those that are resemble someone on an eating binge. Accreting black holes hungrily absorb material around them. Slowly, as they munch on more and more cosmic food, they pull their host galaxies closer together.

“They’re no longer on a diet,” Fu says.

All that eating unleashes a torrent of energy, intense bursts of light called quasars that are so bright they nearly obscure the galaxies themselves. Those quasars should be easy to observe, even at great distances, but most of the light they produce is actually extinguished by the dust brewed up in the merging activity.

Thankfully, supermassive black holes also emit radio waves, and those emissions “come to the rescue because they don’t get extinguished by the dust,” Fu says.

Fu and his team will examine radio-emission maps captured by the Very Large Array, one of the world’s premier astronomical radio observatories, located in New Mexico and operated by the National Radio Astronomy Observatory, an NSF facility. The group will confirm its findings through optical observations at the W.M. Keck Observatory, located on Mauna Kea, a dormant volcano in Hawaii.

The NSF grant also will fund the student-led building of an “augmented reality sandbox” to demonstrate gravity’s influence in the universe, such as on the orbits of planets, the accretion disk around a black hole or neutron star, and the complex orbits of stars in elliptically shaped galaxies.

Nine undergraduates have so far been involved in the project; they divided into teams to write the software programming, build the sandbox (with actual sand), and create an app for Android tablets.

The sandbox will be used in astronomy classes, physics demonstrations for K–12 students in the greater Iowa City area, and exhibitions at the UI Museum of Natural History and the UI Mobile Museum.

The sandbox is expected to be complete by the end of the spring 2017 semester.

“It is quite impressive,” Fu says. “The students may not necessarily like taking exams, but they work really well in teams.”

Source: University of Iowa

Tsunami of Stars and Gas Produces Dazzling Eye-shaped Feature in Galaxy

Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) have discovered a tsunami of stars and gas that is crashing midway through the disk of a spiral galaxy known as IC 2163. This colossal wave of material – which was triggered when IC 2163 recently sideswiped another spiral galaxy dubbed NGC 2207 – produced dazzling arcs of intense star formation that resemble a pair of eyelids.

“Although galaxy collisions of this type are not uncommon, only a few galaxies with eye-like, or ocular, structures are known to exist,” said Michele Kaufman, an astronomer formerly with The Ohio State University in Columbus and lead author on a paper published in the Astrophysical Journal.

Dazzling eyelid-like features bursting with stars in galaxy IC 2163 formed from a tsunami of stars and gas triggered by a glancing collision with galaxy NGC 2207 (a portion of its spiral arm is shown on right side of image). ALMA image of carbon monoxide (orange), which revealed motion of the gas in these features, is shown on top of Hubble image (blue) of the galaxy. Credit: M. Kaufman; B. Saxton (NRAO/AUI/NSF); ALMA (ESO/NAOJ/NRAO); NASA/ESA Hubble Space Telescope

Dazzling eyelid-like features bursting with stars in galaxy IC 2163 formed from a tsunami of stars and gas triggered by a glancing collision with galaxy NGC 2207 (a portion of its spiral arm is shown on right side of image). ALMA image of carbon monoxide (orange), which revealed motion of the gas in these features, is shown on top of Hubble image (blue) of the galaxy. Credit: M. Kaufman; B. Saxton (NRAO/AUI/NSF); ALMA (ESO/NAOJ/NRAO); NASA/ESA Hubble Space Telescope

Kaufman and her colleagues note that the paucity of similar features in the observable universe is likely due to their ephemeral nature. “Galactic eyelids last only a few tens of millions of years, which is incredibly brief in the lifespan of a galaxy. Finding one in such a newly formed state gives us an exceptional opportunity to study what happens when one galaxy grazes another,” said Kaufman.

The interacting pair of galaxies resides approximately 114 million light-years from Earth in the direction of the constellation Canis Major. These galaxies brushed past each other – scraping the edges of their outer spiral arms – in what is likely the first encounter of an eventual merger.

Using ALMA’s remarkable sensitivity and resolution, the astronomers made the most detailed measurements ever of the motion of carbon monoxide gas in the galaxy’s narrow eyelid features. Carbon monoxide is a tracer of molecular gas, which is the fuel for star formation.

Annotated image showing dazzling eyelid-like features bursting with stars in galaxy IC 2163 formed from a tsunami of stars and gas triggered by a glancing collision with galaxy NGC 2207 (a portion of its spiral arm is shown on right side of image). ALMA image of carbon monoxide (orange), which revealed motion of the gas in these features, is shown on top of Hubble image (blue) of the galaxy. Credit: M. Kaufman; B. Saxton (NRAO/AUI/NSF); ALMA (ESO/NAOJ/NRAO); NASA/ESA Hubble Space Telescope

Annotated image showing dazzling eyelid-like features bursting with stars in galaxy IC 2163 formed from a tsunami of stars and gas triggered by a glancing collision with galaxy NGC 2207 (a portion of its spiral arm is shown on right side of image). ALMA image of carbon monoxide (orange), which revealed motion of the gas in these features, is shown on top of Hubble image (blue) of the galaxy. Credit: M. Kaufman; B. Saxton (NRAO/AUI/NSF); ALMA (ESO/NAOJ/NRAO); NASA/ESA Hubble Space Telescope

The data reveal that the gas in the outer portion of IC 2163’s eyelids is racing inward at speeds in excess of 100 kilometers a second. This gas, however, quickly decelerates and its motion becomes more chaotic, eventually changing trajectory and aligning itself with the rotation of the galaxy rather than continuing its pell-mell rush toward the center.

“What we observe in this galaxy is very much like a massive ocean wave barreling toward shore until it interacts with the shallows, causing it to lose momentum and dump all of its water and sand on the beach,” said Bruce Elmegreen, a scientist with IBM’s T.J. Watson Research Center in Yorktown Heights, New York, and co-author on the paper.

“Not only do we find a rapid deceleration of the gas as it moves from the outer to the inner edge of the eyelids, but we also measure that the more rapidly it decelerates, the denser the molecular gas becomes,” said Kaufman. “This direct measurement of compression shows how the encounter between the two galaxies drives gas to pile up, spawn new star clusters and form these dazzling eyelid features.”

Galaxies IC 2163 (left) and NGC 2207 (right) recently grazed past each other, triggering a tsunami of stars and gas in IC 2163 and producing the dazzling eyelid-like features there. ALMA image of carbon monoxide (orange), which revealed motion of the gas in these features, is shown on top of Hubble image (blue) of the galaxy pair. Credit: M. Kaufman; B. Saxton (NRAO/AUI/NSF); ALMA (ESO/NAOJ/NRAO); NASA/ESA Hubble Space Telescope

Galaxies IC 2163 (left) and NGC 2207 (right) recently grazed past each other, triggering a tsunami of stars and gas in IC 2163 and producing the dazzling eyelid-like features there. ALMA image of carbon monoxide (orange), which revealed motion of the gas in these features, is shown on top of Hubble image (blue) of the galaxy pair. Credit: M. Kaufman; B. Saxton (NRAO/AUI/NSF); ALMA (ESO/NAOJ/NRAO); NASA/ESA Hubble Space Telescope

The authors continue to study this galaxy pair and currently are comparing the properties (e.g., locations, ages, and masses) of the star clusters previously observed with NASA’s Hubble Space Telescope with the properties of the molecular clouds observed with ALMA. They hope to better understand the differences between molecular clouds and star clusters in the eyelids and those elsewhere in the galaxy pair.

Source: NRAO

 

Chandra finds Galactic Particle Accelerator, Black Hole Bonanza

Astronomers using NASA’s Chandra X-ray Observatory are uncovering secrets of some of the most mysterious and exciting X-ray spewing objects in the universe. Here are two latest findings presented at the 229th American Astronomical Society meeting in Grapevine, Texas this week.

Astronomers Discover Powerful Cosmic Double Whammy

Astronomers have discovered a cosmic one-two punch unlike any ever seen before. Two of the most powerful phenomena in the Universe, a supermassive black hole, and the collision of giant galaxy clusters, have combined to create a stupendous cosmic particle accelerator.

Abell 3411 and Abell 3412: A pair of colliding galaxies about 2 billion light years away.
Credits: X-ray: NASA/CXC/SAO/R. van Weeren et al; Optical: NAOJ/Subaru; Radio: NCRA/TIFR/GMRT

By combining data from Chandra, the Giant Metrewave Radio Telescope (GMRT) in India, the NSF’s Karl G. Jansky Very Large Array, and other telescopes, researchers have found out what happens when matter ejected by a giant black hole is swept up in the merger of two enormous galaxy clusters.

Read more from NASA’s Chandra X-ray Observatory

Deepest X-ray Image Ever Reveals Black Hole Treasure Trove

An unparalleled image from Chandra gives astronomers the best look yet at the growth of black holes over billions of years beginning soon after the Big Bang. This is the deepest X-ray image ever obtained, collected with about 7 million seconds, or eleven and a half weeks, of Chandra observing time.

The image comes from what is known as the Chandra Deep Field-South. The central region of the image contains the highest concentration of supermassive black holes ever seen, equivalent to about 5,000 objects that would fit into the area of the full Moon and about a billion over the entire sky.

Chandra Deep Field-South: The deepest X-ray image, containing objects at a distance of nearly 13 billion light years. Credits: X-ray: NASA/CXC/Penn State/B.Luo et al.

Read more from NASA’s Chandra X-ray Observatory

 

Source: NASA

 

Deepest x-ray image ever reveals black hole treasure trove

An unparalleled image from NASA’s Chandra X-ray Observatory is giving an international team of astronomers the best look yet at the growth of black holes over billions of years beginning soon after the Big Bang. This is the deepest X-ray image ever obtained, collected with about 7 million seconds, or 11 and a half weeks, of Chandra observing time.

The image comes from what is known as the Chandra Deep Field-South. The central region of the image contains the highest concentration of supermassive black holes ever seen, equivalent to about 5,000 objects that would fit into the area of the full Moon and about a billion over the entire sky.

“With this one amazing picture, we can explore the earliest days of black holes in the Universe and see how they change over billions of years,” said Niel Bradt, the Verne M. Willaman Professor of Astronomy and Astrophysics, and professor of physics, Penn State, who led a team of astronomers studying the deep image.

The image is from the Chandra Deep Field-South. The full field covers an approximately circular region on the sky with an area about two-thirds that of the full Moon. However, the outer regions of the image, where the sensitivity to X-ray emission is lower, are not shown here. The colors in this image represent different levels of X-ray energy detected by Chandra. Here the lowest-energy X-rays are red, the medium band is green, and the highest-energy X-rays observed by Chandra are blue. The central region of this image contains the highest concentration of supermassive black holes ever seen, equivalent to about 5,000 objects that would fit into the area of the full Moon and about a billion over the entire sky. Image credit: X-ray: NASA/CXC/Penn State/B. Luo et al

About 70 percent of the objects in the new image are supermassive black holes, which may range in mass from about 100,000 to 10 billion times the mass of the Sun. Gas falling towards these black holes becomes much hotter as it approaches the event horizon, or point of no return, producing bright X-ray emission.

“It can be very difficult to detect black holes in the early Universe because they are so far away and they only produce radiation if they’re actively pulling in matter,” said team member Bin Luo, professor of astronomy and space science, Nanjing University. “But by staring long enough with Chandra, we can find and study large numbers of growing black holes, some of which appear not long after the Big Bang.”

The new ultra-deep X-ray image allows scientists to explore ideas about how supermassive black holes grew about one to two billion years after the Big Bang. Using these data, the researchers showed that these black holes in the early Universe grow mostly in bursts, rather than via the slow accumulation of matter.

The researchers also have found hints that the seeds for supermassive black holes may be “heavy” with masses about 10,000 to 100,000 times that of the Sun, rather than light seeds with about 100 times the Sun’s mass. This addresses an important mystery in astrophysics about how these objects can grow so quickly to reach masses of about a billion times the Sun in the early Universe.

They also have detected X-rays from massive galaxies at distances up to about 12.5 billion light years from Earth. Most of the X-ray emission from the most distant galaxies likely comes from large collections of stellar-mass black holes within the galaxies. These black holes are formed from the collapse of massive stars and typically weigh a few to a few dozen times the mass of the Sun.

“By detecting X-rays from such distant galaxies, we’re learning more about the formation and evolution of stellar-mass and supermassive black holes in the early Universe,” said team member Fabio Vito, postdoctoral scholar in astronomy and astrophysics, Penn State. “We’re looking back to times when black holes were in crucial phases of growth, similar to hungry infants and adolescents.”

To perform this study, the team combined the Chandra X-ray data with very deep Hubble Space Telescope data over the same patch of sky. They studied X-ray emission from over 2,000 galaxies identified by Hubble that are located between about 12 and 13 billion light years from Earth.

Further work using Chandra and future X-ray observatories will be needed to provide a definite solution to the mystery of how supermassive black holes can quickly reach large masses. A larger sample of distant galaxies will come from observations with the James Webb Space Telescope, extending the study of X-ray emission from black holes out to even greater distances from Earth.

Source: Penn State University