Arecibo observatory: Two New Programs Launching to Listen for Aliens

The 305-meter telescope at Arecibo Observatory is just one of a collection that SETI will use to search nearby stars for electronic signals that could indicate intelligent life. 

If such a civilization was utilizing a similar dish to image exoplanets, SETI's team should be able to detect it.

Credit: Arecibo Observatory

SETI is stepping up its search for alien lifeforms on far off worlds.

The Search for Extraterrestrial Intelligence (SETI) program recently announced two new methods to search for signals that could come from life on other planets.

In the Panchromatic SETI project, multiple telescopes will scan a variety of wavelengths from 30 stars near the sun; the project will look for powerful signals beamed into space, potentially by intelligent extraterrestrials.

SETI is also launching an interplanetary eavesdropping program that is expected to search for messages beamed between planets in a single system.

"If we are polluting space, perhaps other extraterrestrials are leaking signals," Dan Werthimer, director of the Berkley SETI Research Center, told an audience during the Smithsonian Magazine's "The Future is Here" Festival in May. "Maybe they're sending something our way."

'Everything we've got'
Since humans made their first FM radio and television transmissions, signals from Earth have been spilling out into space, announcing the presence of intelligent life to any group that might be searching for it.

According to Werthimer, signals from the 1950s television show "I Love Lucy" have reached thousands of stars, while the nearest suns have already enjoyed the "The Simpsons."

If Earth has unintentionally leaked signs of its presence, other alien civilizations may have done the same thing.

SETI's new Panchromatic project will utilize a variety of telescopes covering a range of frequencies to scour the nearest stars.

"We're going to throw everything we've got at it," Werthimer added.

The panchromatic project will examine a sample of the 30 stars that lie within 5 parsecs (16 light-years) from the sun. The list includes 13 single stars, seven binary systems and one triple system.

Most of the stars are smaller than the sun, but the project will also examine two white dwarfs and one moderately evolved F star. No confirmed exoplanets have been found around any of the stars.

By setting distance as the criteria, the SETI team hopes to alleviate any bias that might otherwise result from focusing on systems similar to that of Earth. The team selected stars for study based only on how far they lie from the sun.

According to SETI-Berkeley's Andrew Siemion, chief scientist of the eavesdropping project, the search will also probe a diverse stellar population already well studied at many wavelengths.

"In the event of a non-detection, these attributes of the sample will allow us to place strong and broadly applicable limits on the presence of technology," Siemion told Space.com via email.

Observations from the Low Frequency Array (LOFAR) telescope in Europe and the Green Bank Telescope (GBT) in West Virginia will begin over the summer and fall of 2014.

Instrument development and commissioning is still in progress for the Infrared Spatial Interferometer (ISI) at Mount Wilson Observatory and the Nickel Telescope at Lick Observatory, both in California.

But according to Siemion, the pair should be ready at about the same time. The Nickel Telescope will conduct the first-ever SETI observations done in the near-infrared.

Remarkable white dwarf star; coldest, dimmest ever detected

This is an artist impression of a white dwarf star in orbit with pulsar PSR J2222-0137. 

It may be the coolest and dimmest white dwarf ever identified. 

Credit: B. Saxton (NRAO /AUI /NSF)

A team of astronomers has identified possibly the coldest, faintest white dwarf star ever detected.

This ancient stellar remnant is so cool that its carbon has crystallized, forming an Earth-size diamond in space.

David Kaplan

"It's a really remarkable object," said David Kaplan, a professor at the University of Wisconsin-Milwaukee. "These things should be out there, but because they are so dim they are very hard to find."

Kaplan and his colleagues found this stellar gem using the National Radio Astronomy Observatory's (NRAO) Green Bank Telescope (GBT) and Very Long Baseline Array (VLBA), as well as other observatories.

White dwarfs are the extremely dense end-states of stars like our Sun that have collapsed to form an object approximately the size of the Earth.

Composed mostly of carbon and oxygen, white dwarfs slowly cool and fade over billions of years. The object in this new study is likely the same age as the Milky Way, approximately 11 billion years old.

Pulsars are rapidly spinning neutron stars, the superdense remains of massive stars that have exploded as supernovas.

As neutron stars spin, lighthouse-like beams of radio waves, streaming from the poles of its powerful magnetic field, sweep through space.

When one of these beams sweeps across the Earth, radio telescopes can capture the pulse of radio waves.

The pulsar companion to this white dwarf, dubbed PSR J2222-0137, was the first object in this system to be detected.

Jason Boyles

It was found using the GBT by Jason Boyles, then a graduate student at West Virginia University in Morgantown.

These first observations revealed that the pulsar was spinning more than 30 times each second and was gravitationally bound to a companion star, which was initially identified as either another neutron star or, more likely, an uncommonly cool white dwarf. The two were calculated to orbit each other once every 2.45 days.

The pulsar was then observed over a two-year period with the VLBA by Adam Deller, an astronomer at the Netherlands Institute for Radio Astronomy (ASTRON).

These observations pinpointed its location and distance from the Earth, approximately 900 light-years away in the direction of the constellation Aquarius.

This information was critical in refining the model used to time the arrival of the pulses at the Earth with the GBT.

By applying Einstein's theory of relatively, the researchers studied how the gravity of the companion warped space, causing delays in the radio signal as the pulsar passed behind it.

These delayed travel times helped the researchers determine the orientation of their orbit and the individual masses of the two stars.

The pulsar has a mass 1.2 times that of the Sun and the companion a mass 1.05 times that of the Sun.

These data strongly indicated that the pulsar companion could not have been a second neutron star; the orbits were too orderly for a second supernova to have taken place.

Knowing its location with such high precision and how bright a white dwarf should appear at that distance, the astronomers believed they should have been able to observe it in optical and infrared light.

Remarkably, neither the Southern Astrophysical Research (SOAR) telescope in Chile nor the 10-meter Keck telescope in Hawaii was able to detect it.

"Our final image should show us a companion 100 times fainter than any other white dwarf orbiting a neutron star and about 10 times fainter than any known white dwarf, but we don't see a thing," said Bart Dunlap, a graduate student at the University of North Carolina at Chapel Hill and one of the team members.

"If there's a white dwarf there, and there almost certainly is, it must be extremely cold."

The researchers calculated that the white dwarf would be no more than a comparatively cool 3,000 degrees Kelvin (2,700 degrees Celsius).

Astronomers believe that such a cool, collapsed star would be largely crystallized carbon, not unlike a diamond.

Other such stars have been identified and they are theoretically not that rare, but with a low intrinsic brightness, they can be deucedly difficult to detect.

Its fortuitous location in a binary system with a neutron star enabled the team to identify this one.

Green Bank Telescope (GBT): High Velocity Smith Cloud is a failed Dwarf Star

This is a false-colour image of the Smith Cloud made with data from the Green Bank Telescope (GBT). 

Credit: NRAO/AUI/NSF

Like a bullet wrapped in a full metal jacket, a high-velocity hydrogen cloud hurtling toward the Milky Way appears to be encased in a shell of dark matter, according to a new analysis of data from the National Science Foundation's Robert C. Byrd Green Bank Telescope (GBT).

Astronomers believe that without this protective shell, the high-velocity cloud (HVC) known as the Smith Cloud would have disintegrated long ago when it first collided with the disk of our Galaxy.

If confirmed by further observations, a halo of dark matter could mean that the Smith Cloud is actually a failed dwarf galaxy, an object that has all the right stuff to form a true galaxy, just not enough to produce stars.

"The Smith Cloud is really one of a kind. It's fast, quite extensive, and close enough to study in detail," said Matthew Nichols with the Sauverny Observatory in Switzerland and principal author on a paper accepted for publication in the Monthly Notices of the Royal Astronomical Society.

"It's also a bit of a mystery; an object like this simply shouldn't survive a trip through the Milky Way, but all the evidence points to the fact that it did."

Previous studies of the Smith Cloud revealed that it first passed through our Galaxy many millions of years ago.

By re-examining and carefully modeling the cloud, astronomers now believe that the Smith Cloud contains and is actually wrapped in a substantial "halo" of dark matter, the gravitationally significant yet invisible stuff that makes up roughly 80 percent of all the matter in the Universe.

"Based on the currently predicted orbit, we show that a dark matter free cloud would be unlikely to survive this disk crossing," observed Jay Lockman, an astronomer at the National Radio Astronomy Observatory in Green Bank, West Virginia, and one of the coauthors on the paper.

"While a cloud with dark matter easily survives the passage and produces an object that looks like the Smith Cloud today."

The Milky Way is swarmed by hundreds of high-velocity clouds, which are made up primarily of hydrogen gas that is too rarefied to form stars in any detectable amount.

The only way to observe these objects, therefore, is with exquisitely sensitive radio telescopes like the GBT, which can detect the faint emission of neutral hydrogen.

If it were visible with the naked eye, the Smith Cloud would cover almost as much sky as the constellation Orion.

Most high-velocity clouds share a common origin with the Milky Way, either as the leftover building blocks of galaxy formation or as clumps of material launched by supernovas in the disk of the Galaxy.

A rare few, however, are interlopers from farther off in space with their own distinct pedigree. A halo of dark matter would strengthen the case for the Smith Cloud being one of these rare exceptions.

Currently, the Smith Cloud is about 8,000 light-years away from the disk of our Galaxy. It is moving toward the Milky Way at more than 150 miles per second and is predicted to impact again in approximately 30 million years.

"If confirmed to have dark matter this would in effect be a failed galaxy," said Nichols. "Such a discovery would begin to show the lower limit of how small a galaxy could be."

The researchers believe this could also improve our understanding of the Milky Way's earliest star formation.

More information: Paper on Arxiv: arxiv.org/abs/1404.3209

Remarkable Features below the surface of the Moon

Mare Serenitatis / Sea of Serenity. 

Credit: Bruce Campbell (Smithsonian Institution, National Air and Space Museum); Arecibo /NAIC; NRAO /AUI /NSF

New images of Earth's Moon reveal more than can be seen with the naked eye, thanks to the combined efforts of the two largest radio telescopes of their kind, the National Radio Astronomy Observatory's Green Bank Telescope (GBT) in West Virginia and the Arecibo Observatory in Puerto Rico.

To make these images, radar signals beamed from Arecibo's powerful transmitter penetrated far below the Moon's dusty surface.

The signals then rebounded back and were picked up by the sensitive receivers on the GBT.

This observing technique, known as bistatic radar, has been used to study many objects in our solar system, including asteroids and other planets.

The first image reveals previously hidden features around an area known as Mare Serenitatis, or the Sea of Serenity, which is near the Apollo 17 landing site.

The radar observations were able to "see" approximately 10-15 meters (33-50 feet) below the lunar surface.

The light and dark features are the result of compositional changes in the lunar dust and differences in the abundance of rocks buried within the soil.

The second image is a similar observation of the lunar impact crater known as Aristillus.

The radar echoes reveal geologic features of the large debris field created by the force of the impact.

The dark "halo" surrounding the crater is due to pulverized debris beyond the rugged, radar-bright rim deposits.

The image also shows traces of lava-like features produced when lunar rock melted from the heat of the impact.

The crater is approximately 55 kilometers (34 miles) in diameter and 3.5 kilometers (2 miles) deep.

Aristillus Crater. 

Credit: Bruce Campbell (Smithsonian Institution, National Air and Space Museum); Arecibo/NAIC; NRAO/AUI/NSF

These images help planetary scientists interpret the complex history of the Moon, which is often obscured by dust layers built up over billions of years, better understand the geology of earlier landing sites, and plan for future lunar exploration.

Fireworks Galaxy: Rivers of Hydrogen Gas Fuel Spiral Galaxies

Three distinct features are visible in this composite image of NGC 6946. 

The bright heart of the galaxy in optical light (blue), the dense hydrogen in the spirals (orange), and the extended halo surrounding the galaxy (red). 

New research also shows a faint filament that could be hydrogen flowing from the intergalactic medium into the galaxy to fuel star formation.

Credit: D.J. Pisano (WVU); B. Saxton (NRAO/AUI/NSF); Palomar Observatory – Space Telescope Science Institute 2nd Digital Sky Survey (Caltech); Westerbork Synthesis Radio Telescope

Inpouring rivers of hydrogen gas could explain how spiral galaxies maintain the constant star formation that dominates their hearts, a new study reports.

Using the Green Bank Telescope (GBT) in West Virginia, scientists observed a tenuous filament of gas streaming into the galaxy NGC 6946, known as the "Fireworks Galaxy" because of the large number of supernovae observed within it.

The find may provide insight into the source of fuel that powers the ongoing birth of young stars, researchers said.

D.J. Pisano

"We knew that the fuel for star formation had to come from somewhere," study lead author D.J. Pisano, of West Virginia University (WVU), said in a statement.

"So far, however, we've detected only about 10 percent of what would be necessary to explain what we observe in many galaxies."

Located 22 million light-years from Earth on the border of the constellations Cepheus and Cygnus, NGC 6946 is a medium-sized spiral galaxy pointed face-on toward the Milky Way.

Previous studies revealed a halo of hydrogen gas around NGC 6946 common to spiral galaxies.

Such halos are formed by hydrogen ejected from the galaxies by star formation and violent supernova explosions.

These interactions heat the gas in the halo to extreme temperatures.

When Pisano turned the GBT toward the spiral galaxy for further examination, however, he discovered a ribbon of gas too cool to have suffered the heating processes undergone by the halo gas.

On average, the Milky Way churns out between 1 to 5 new stars per year. Rich in gas, NGC 6946 is far more active. For example, it has hosted at least 9 explosive supernovae in the past century.

"A leading theory is that rivers of hydrogen — known as cold flows — may be ferrying hydrogen through intergalactic space, clandestinely fueling star formation," Pisano said. "But this tenuous hydrogen has simply been too diffuse to detect, until now."

The immense, unblocked dish of the Green Bank Telescope (GBT), combined with its location in the US National Radio Quiet Zone, where radio transmissions are limited, allow the large disk to detect the faint hydrogen signal that would be present in a cold flow.

Another possibility is that the hydrogen detected originated from a close encounter with another galaxy in the past.

The gravitational interaction between the two could have stretched out a ribbon of neutral atomic hydrogen, researchers said.

Such a ribbon would contain stars that astronomers should be able to easily observe, though none have yet been spotted. Further studies of the streamer hydrogen gas will help clarify its role.

The research was published in the Astronomical Journal.

Green Bank Telescope (GBT): River of Hydrogen flowing through space

This composite image contains three distinct features: the bright star-filled central region of galaxy NGC 6946 in optical light (blue), the dense hydrogen tracing out the galaxy's sweeping spiral arms and galactic halo (orange), and the extremely diffuse and extended field of hydrogen engulfing NGC 6946 and its companions (red). 

The new GBT data show the faintly glowing hydrogen bridging the gulf between the larger galaxy and its smaller companions. 

This faint structure is precisely what astronomers expect to appear as hydrogen flows from the intergalactic medium into galaxies or from a past encounter between galaxies. 

Credit: D.J. Pisano (WVU); B. Saxton (NRAO/AUI/NSF); Palomar Observatory -- Space Telescope Science Institute 2nd Digital Sky Survey (Caltech); Westerbork Synthesis Radio Telescope (WSRT)

D.J. Pisano

Using the National Science Foundation's Robert C. Byrd Green Bank Telescope (GBT), astronomer D.J. Pisano from West Virginia University has discovered what could be a never-before-seen river of hydrogen flowing through space.

This very faint, very tenuous filament of gas is streaming into the nearby galaxy NGC 6946 and may help explain how certain spiral galaxies keep up their steady pace of star formation.

"We knew that the fuel for star formation had to come from somewhere. So far, however, we've detected only about 10 percent of what would be necessary to explain what we observe in many galaxies," said Pisano.

"A leading theory is that rivers of hydrogen – known as cold flows – may be ferrying hydrogen through intergalactic space, clandestinely fueling star formation. But this tenuous hydrogen has been simply too diffuse to detect, until now."

Spiral galaxy NGC 6946

Spiral galaxies, like our own Milky Way, typically maintain a rather tranquil but steady pace of star formation.

Others, like NGC 6946, which is located approximately 22 million light-years from Earth on the border of the constellations Cepheus and Cygnus, are much more active, though less-so than more extreme starburst galaxies.

This raises the question of what is fueling the sustained star formation in this and similar spiral galaxies.

Earlier studies of the galactic neighborhood around NGC 6946 with the Westerbork Synthesis Radio Telescope (WSRT) in the Netherlands have revealed an extended halo of hydrogen (a feature commonly seen in spiral galaxies, which may be formed by hydrogen ejected from the disk of the galaxy by intense star formation and supernova explosions).

A cold flow, however, would be hydrogen from a completely different source: gas from intergalactic space that has never been heated to extreme temperatures by a galaxy's star birth or supernova processes.

Using the GBT, Pisano was able to detect the glow emitted by neutral hydrogen gas connecting NGC 6946 with its cosmic neighbours. This signal was simply below the detection threshold of other telescopes.

The GBT's unique capabilities, including its immense single dish, unblocked aperture, and location in the National Radio Quiet Zone, enabled it to detect this tenuous radio light.

Astronomers have long theorized that larger galaxies could receive a constant influx of cold hydrogen by syphoning it off other less-massive companions.

In looking at NGC 6946, the GBT detected just the sort of filamentary structure that would be present in a cold flow, though there is another probable explanation for what has been observed.

It's also possible that sometime in the past this galaxy had a close encounter and passed by its neighbours, leaving a ribbon of neutral atomic hydrogen in its wake.

If that were the case, however, there should be a small but observable population of stars in the filaments.

Further studies will help to confirm the nature of this observation and could shine light on the possible role that cold flows play in the evolution of galaxies.

Journal Reference: D. J. Pisano. GREEN BANK TELESCOPE OBSERVATIONS OF LOW COLUMN DENSITY H I AROUND NGC 2997 AND NGC 6946. The Astronomical Journal, 2014; 147 (3): 48 DOI: 10.1088/0004-6256/147/3/48

GBT NRAO: Pulsar in stellar triple system makes unique gravitational laboratory

The pulsar (L) is orbited by a hot white dwarf star (C) both of which are orbited by a cooler, distant white dwarf (R)

Credit: NRAO

Astronomers using the National Science Foundation's Green Bank Telescope (GBT) have discovered a unique stellar system of two white dwarf stars and a superdense neutron star, all packed within a space smaller than Earth's orbit around the Sun.

The results appear in Nature journal and will be presented at the 223rd American Astronomical Society meeting.

The closeness of the stars, combined with their nature, has allowed the scientists to make the best measurements yet of the complex gravitational interactions in such a system.

In addition, detailed studies of this system may provide a key clue for resolving one of the principal outstanding problems of fundamental physics—the true nature of gravity.

"This triple system gives us a natural cosmic laboratory far better than anything found before for learning exactly how such three-body systems work and potentially for detecting problems with General Relativity that physicists expect to see under extreme conditions," said Scott Ransom of the National Radio Astronomy Observatory (NRAO).

West Virginia University graduate student Jason Boyles (now at Western Kentucky University) originally uncovered the pulsar as part of a large-scale search for pulsars with the GBT.

Pulsars are neutron stars that emit lighthouse-like beams of radio waves that rapidly sweep through space as the object spins on its axis.

GALEX satellite

One of the search's discoveries was a pulsar some 4200 light-years from Earth, spinning nearly 366 times per second.

Such rapidly-spinning pulsars are called millisecond pulsars, and can be used by astronomers as precision tools for studying a variety of phenomena, including searches for the elusive gravitational waves.

Subsequent observations showed that the pulsar is in a close orbit with a white dwarf star, and that pair is in orbit with another, more-distant white dwarf.

WIYN NRAO Telescope

"This is the first millisecond pulsar found in such a system, and we immediately recognized that it provides us a tremendous opportunity to study the effects and nature of gravity," Ransom said.

The scientists began an intensive observational program using the GBT, the Arecibo radio telescope in Puerto Rico, and the Westerbork Synthesis Radio Telescope in the Netherlands.

They also studied the system using data from the Sloan Digital Sky Survey, the GALEX satellite, the WIYN telescope on Kitt Peak, Arizona, and the Spitzer Space Telescope.

"The gravitational perturbations imposed on each member of this system by the others are incredibly pure and strong," Ransom said.

"The millisecond pulsar serves as an extremely powerful tool for measuring those perturbations incredibly well," he added.

More information: Nature DOI: 10.1038/nature12917

Green Bank Telescope: Hidden details revealed in nearby starburst galaxy

This composite image of starburst galaxy M82 shows the distribution of dense molecular gas as seen by the GBT (yellow and red) and the background stars and dust as seen by the Hubble Space telescope (blue).

The yellow areas correspond to regions of intense star formation.

The red areas trace outflows of gas from the disk of the galaxy. 

Credit: Bill Saxton (NRAO/AUI/NSF); Hubble/NASA

Using the new, high-frequency capabilities of the National Science Foundation's Robert C. Byrd Green Bank Telescope (GBT), astronomers have captured never-before-seen details of the nearby starburst galaxy M82.

These new data highlight streamers of material fleeing the disk of the galaxy as well as concentrations of dense molecular gas surrounding pockets of intense star formation.

M82, which is located approximately 12 million light-years away in the constellation Ursa Major, is a classic example of a starburst galaxy—one that is producing new stars tens- to hundreds-of-times faster than our own Milky Way.

Its relatively nearby location made it an ideal target for the GBT's newly equipped "W-Band" receiver, which is capable of detecting the millimeter wavelength light that is emitted by molecular gas.

This new capability makes the GBT the world's largest single-dish, millimeter-wave telescope.

Amanda Kepley

"With this new vision, we were able to look at M82 to explore how the distribution of molecular gas in the galaxy corresponded to areas of intense star formation," said Amanda Kepley, a post-doctoral fellow at the National Radio Astronomy Observatory (NRAO) in Green Bank, West Virginia, and lead author on a paper accepted for publication in the Astrophysical Journal Letters.

"Having this new capability may help us understand why stars form where they do."

Astronomers recognize that dense molecular gas goes hand-in-hand with areas of star formation, but the connection is poorly understood and this relationship may be different in different types of galaxies.

By creating wide-angle maps of the gas in galaxies, astronomers hope to better understand this complex interplay.

To date, however, these kinds of observations have not been easy since molecules that are used to map the distribution of dense gas, like HCN (hydrogen cyanide) and HCO+ (formylium), shine feebly in millimeter light.

With its new W-Band receiver, the GBT was able to make highly sensitive, wide-angle images of these gases in and around M82.

"The GBT data clearly show billowing concentrations of dense molecular gas huddled around areas that are undergoing bursts of intense star formation," said Kepley.

"They also reveal giant outflows of ionized gas fleeing the disk of the galaxy. These outflows are driven by star formation deep within the galaxy."

This capability will enable astronomers to quickly survey entire galaxies and different parts within galaxies.

Such surveys would complement higher resolution observations with new Atacama Large Millimeter/submillimeter Array (ALMA) telescope in Chile.

The 100-meter GBT is located in the National Radio Quiet Zone and the West Virginia Radio Astronomy Zone, which protect the incredibly sensitive telescope from unwanted radio interference.

Numerous Hydrogen Clouds discovered lurking among our galactic neighbours

This combined graphic shows new, high-resolution GBT imaging (in box) of recently discovered hydrogen clouds between M31 (upper right) and M33 (bottom left). 

Credit: Bill Saxton, NRAO/AUI/NSF

In a dark, starless patch of intergalactic space, astronomers have discovered a never-before-seen cluster of hydrogen clouds strewn between two nearby galaxies, Andromeda (M31) and Triangulum (M33).

The researchers speculate that these rarefied blobs of gas—each about as massive as a dwarf galaxy—condensed out of a vast and as-yet undetected reservoir of hot, ionized gas, which could have accompanied an otherwise invisible band of dark matter.

The astronomers detected these objects using the National Science Foundation's Green Bank Telescope (GBT) at the National Radio Astronomy Observatory (NRAO) in Green Bank, W.Va. The results were published in the journal Nature.

Spencer Wolfe

"We have known for some time that many seemingly empty stretches of the Universe contain vast but diffuse patches of hot, ionized hydrogen," said Spencer Wolfe of West Virginia University in Morgantown.

"Earlier observations of the area between M31 and M33 suggested the presence of colder, neutral hydrogen, but we couldn't see any details to determine if it had a definitive structure or represented a new type of cosmic feature."

"Now, with high-resolution images from the GBT, we were able to detect discrete concentrations of neutral hydrogen emerging out of what was thought to be a mainly featureless field of gas."

Astronomers are able to observe neutral atomic hydrogen, which is referred to as HI (H and the Roman numeral one), because of the characteristic signal it emits at radio wavelengths, which can be detected by radio telescopes on Earth.

Though this material is abundant throughout the cosmos, in the space between galaxies it can be very tenuous and the faint signal it emits can be extremely difficult to detect.



The animation demonstrates the difference in resolution from the original Westerbork Radio Telescope data (Braun & Thilker, 2004) and the finer resolution imaging of GBT, which revealed the hydrogen clouds between M31 and M33. 

Credit: Bill Saxton, NRAO/AUI/NSF.

A little more than a decade ago, astronomers had the first speculative hints that a previously unrecognized reservoir of hydrogen lay between M31 and M33.

The signal from this gas, however, was too faint to draw any firm conclusions about its nature, origin, or even certain existence.

Last year, preliminary data taken with the GBT confirmed that there was indeed hydrogen gas, and a lot of it, smeared out between the galaxies.

These preliminary observations, however, lacked the necessary sensitivity to see any fine-grain structure in the gas or deduce whence it came and what it signified.

The most likely explanation at the time was that a few billion years earlier, these two galaxies had a close encounter and the resulting gravitational perturbations pulled off some wispy puffs of gas, leaving a tenuous bridge between the two.