A screenshot from "The Observatories", a video of mainly Australian astronomical observatories. Credit: Alex Cherney/Vimeo
Performing observations in Australia is on many astronomers’ bucket lists, and this video timelapse shows you precisely why. Famous, world-class observatories, dark sky and the beautiful desolation of the desert combine in this award-winning sequence shot by Alex Cherney and posted on Vimeo.
Cherney writes that the video “is the result of over three years of work” and was the winner of the 2014 STARMUS astrophotography competition. Here are the observatories that are featured:
Roque De Los Muchachos Observatory, La Palma;
Australian Square Kilometre Array Pathfinder, Murchison, Australia;
Australia Telescope Compact Array, Narrarbri, Australia;
Comet ISON was one of the two comets studied by scientists using the Atacama Large Millimeter/submillimeter Array (ALMA). The diagram shows where it was located in the solar system at the time of observations. 3-D images of its coma (atmosphere) revealed organic compounds. Credit: B. Saxton (NRAO/AUI/NSF); NASA/ESA Hubble; M. Cordiner, NASA, et al.
While Comet ISON’s breakup around Thanksgiving last year disappointed many amateur observers, its flight through the inner solar system beforehand showed scientists something neat: it was carrying organic materials with it.
A group examined the molecules surrounding the comet in its coma (atmosphere) and, along with observations of Comet Lemmon, created a 3-D model that you can see above. Among other results, this revealed the presence of formaldehyde and HNC (hydrogen, nitrogen and carbon). The formaldehyde was expected, but the spot where HNC was found came as a surprise.
Scientists used to think that HNC is produced from the nucleus, but the research revealed that it actually happens when larger molecules or organic dust breaks down in the coma.
“Understanding organic dust is important, because such materials are more resistant to destruction during atmospheric entry, and some could have been delivered intact to early Earth, thereby fueling the emergence of life,” stated Michael Mumma, a co-author on the study who is director of the Goddard Center for Astrobiology. “These observations open a new window on this poorly known component of cometary organics.”
Observation were made possible using the powerful Atacama Large Millimeter/submillimeter Array (ALMA). The array of 66 radio telescopes in Chile allows astronomers to map molecules and peer past dust clouds in star systems under formation, among other things. ALMA was completed last year and is the largest telescope of its type in the world.
The array’s resolution allowed scientists to probe for these molecules in moderately bright comets, which is also new. Previously, these types of studies were limited to “blockbuster” visitors such as Comet Hale-Bopp in the 1990s, NASA sated.
The study, which was led by the Goddard Center for Astrobiology’s Martin Cordiner at NASA’s Goddard Space Flight Center, was published in Astrophysical Journal Letters. The research is also available in preprint version on Arxiv.
Image of the sky where the radio burst FRB 121102 was found, in the constellation Auriga. You can see its location with a green circle. At left is supernova remnant S147 and at right, a star formation area called IC 410. Credit: Rogelio Bernal Andreo (DeepSkyColors.com)
Where are these radio bursts coming from? Astronomers have heard these signals from the sky several times, but always with the same telescope (Parkes Observatory in Australia). There was debate about whether these were coming from inside or outside the galaxy, or even from Earth itself (given only the one observatory was detecting them.)
A new study with a different telescope, the Arecibo Observatory in Puerto Rico, concludes that the bursts are from outside the galaxy. This is the first time one of these bursts have been found in the northern hemisphere of the sky.
“Our result is important because it eliminates any doubt that these radio bursts are truly of cosmic origin,” stated Victoria Kaspi, an astrophysics researcher at McGill University who participated in the research. “The radio waves show every sign of having come from far outside our galaxy – a really exciting prospect.”
Fast radio bursts are a flurry of radio waves that last a few thousandths of a second, and at any given minute there are only seven of these in the sky on average, according to the Max Planck Institute for Radio Astronomy. Their cause is unknown. They could be anything from black holes, to neutron stars coming together, to the magnetic field of pulsars (a type of neutron star) flaring up — or something else.
Arecibo Observatory in Puerto Rico. Credit: NAIC – Arecibo Observatory, a facility of the NSF
The pulse was found Nov. 2, 2012 in the constellation Auriga. Astronomers believe it is from quite far away from measuring its plasma dispersion, or the slowdown of radio waves as they crash into interstellar electrons. This particular source had triple the maximum dispersion than what would be found inside the galaxy, astronomers stated.
“The brightness and duration of this event, and the inferred rate at which these bursts occur, are all consistent with the properties of the bursts previously detected by the Parkes telescope in Australia,” stated Laura Spitler, who led the research. (She was at Cornell University when the study began, but is now at the Max Planck Institute for Radio Astronomy in Bonn, Germany.)
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)
We live in a vast, dark Universe, which makes the smallest and coolest objects extremely difficult to detect, save for a stroke of luck. Often times this luck comes in the form of a companion. Take, for example, the first exoplanet detected due to its orbit around a pulsar — a rapidly spinning neutron star.
A team of researchers using the National Radio Astronomy Observatory’s Green Bank Telescope and the Very Long Baseline Array (VLBA), as well as other observatories have repeated the story, detecting an object in orbit around a distant pulsar. Except this time it’s the coldest, faintest white dwarf ever detected. So cool, in fact, its carbon has crystallized.
The punch line is this: with the help of a pulsar, astronomers have detected an Earth-size diamond in the sky.
“It’s a really remarkable object,” said lead author David Kaplan from the University of Wisconsin-Milwaukee in a press release. “These things should be out there, but because they are so dim they are very hard to find.”
The story begins when Dr. Jason Boyles, then a graduate student at West Virginia University, identified a pulsar, dubbed PSR J2222-0127, 900 light-years away in the constellation Aquarius.
When the core of a massive star runs out of energy, it collapses to form an incredibly dense neutron star or black hole. Bring a teaspoon of neutron star to Earth and it would outweigh Mount Everest at about a billion tons. A pulsar is simply a spinning neutron star.
But as a pulsar spins, lighthouse-like beams of radio waves stream from the poles of its powerful magnetic field. If they sweep past the Earth, they’ll give rise to blips of radio waves, so regular that you could set your watch by them. But if the pulsar carries a companion in tow, the tiny gravitational tugs can offset that timing slightly.
The first observations of PSR J2222-0137 identified that it was spinning more than 30 times each second. It was then observed over a two-year period with the VLBA. By applying Einstein’s theory of relativity — which predicts that light slows in the presence of a gravitational field — the researchers studied how the gravity of the companion warped space, causing delays in the radio signal as the pulsar passed behind it.
The delayed travel times helped the researchers determine the individual masses of the two stars. The pulsar has a mass of 1.2 times that of the Sun and the companion a mass 1.05 times that of the Sun. Previously, researchers had thought the companion was likely another neutron star, or a white dwarf, the remnant of a Sun-like star.
But the timing variations made the neutron star scenario unlikely. The orbits were too orderly for a second supernova to have taken place. So knowing the typical brightness of a white dwarf and its distance, astronomers initially thought they would be able to detect the elusive companion in optical and infrared light.
An image taken in visible light at the SOAR telescope of the field of the pulsar/white dwarf pair. The exact location of the white dwarf is known to a pixel. But it’s not there. Image Credit: NOAO
However, neither the Southern Astrophysical Research 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 coauthor Bart Dunlap, a graduate student at the University of North Carolina. “If there’s a white dwarf there, and there almost certainly is, it must be extremely cold.”
The research team calculated that the white dwarf would be no more than 3,000 degrees Kelvin. At such a low temperature, the collapsed star would be largely crystallized carbon, similar to diamond.
The paper has been accepted for publication in the Astrophysical Journal and may be viewed here.
Radar delay-Doppler images of asteroid 2014 HQ124. The Earth and radar transmitter are toward the top of each frame. Each frame has the same orientation, delay-Doppler dimensions, resolution (3.75 m by 0.0125 Hz), and duration (10 minutes). Arecibo images appear on the top row and Goldstone images appear on the other rows: Arecibo Observatory capabilities eliminated the "snow" visible in the other images.There is a gap of about 35 minutes between rows 1 and 2. Credit: Marina Brozovic and Joseph Jao, Jet Propulsion Laboratory/ Caltech/ NASA/ USRA/ Arecibo Observatory/ NSF
On June 8, the 370-meter (about 1,300-ft.) asteroid 2014 HQ124 breezed by Earth at a distance of just 800,000 miles (1.3 million km). Only hours after closest approach, astronomers used a pair of radio telescopes to produce some of the most detailed images of a near-Earth asteroid ever obtained. They reveal a peanut-shaped world called a ‘contact binary’, an asteroid comprised of two smaller bodies touching.
About one in six asteroids in the near-Earth population has this type of elongated or “peanut” shape. It’s thought that contact binaries form when two or more asteroids get close enough to touch and ‘stick’ together through their mutual gravitational attraction. Asteroid 25143 Itokawa, visited and sampled by the Japanese spacecraft Hayabusa in 2005, is another member of this shapely group.
Radar observations of asteroid 2014 HQ124 seen here in video
The 21 radar images were taken over a span of four hours and reveal a rotation rate of about 20 hours. They also show features as small as about 12 feet (3.75 meters) wide. This is the highest resolution currently possible using scientific radar antennas to produce images. Such sharp views were made possible for this asteroid by linking together two giant radio telescopes to enhance their capabilities.
Astronomers used the 230-foot (70-meter) Deep Space Network antenna at Goldstone, Calif. to beam radar signals at the asteroid which reflected them back to the much larger 1000-foot (305-meter) Arecibo dish in Puerto Rico. The technique greatly increases the amount of detail visible in radar images.
Aerial view of the 1,000-foot dish at Arecibo Observatory. Credit: NOAA
Arecibo Observatory and Goldstone radar facilities are unique for their ability to resolve features on asteroids, while most optical telescopes on the ground would see these cosmic neighbors simply as unresolved points of light. The radar images reveal a host of interesting features, including a large depression on the larger lobe as well as two blocky, sharp-edged features at the bottom on the radar echo (crater wall?) and a small protrusion along its long side that looks like a mountain. Scientists suspect that some of the bright features visible in multiple frames could be surface boulders.
“These radar observations show that the asteroid is a beauty, not a beast”, said Alessondra Springmann, a data analyst at Arecibo Observatory.
A single radar image frame close-up view of 2014 HQ124. Credit: NASA
The first five images in the sequence (top row in the montage) represent the data collected by Arecibo, and demonstrate that these data are 30 times brighter than what Goldstone can produce observing on its own. There’s a gap of about 35 minutes between the first and second rows in the montage, representing the time needed to switch from receiving at Arecibo to receiving at the smaller Goldstone station.
If you relish up-close images of asteroids as much as I do, check out NASA’s Asteroid Radar Research site for more photos and information on how radar pictures are made.
Imagine you’re a researcher at a cocktail party. You meet Carl Sagan (Carl Sagan!) and he hands you a novel. And it turns out that you are the inspiration for the major character in that book.
What was SETI researcher Jill Tarter’s reaction when this actually happened and she heard about Ellie, the protagonist in Contact?
“I said, ‘Look. Here’s the deal. As long as she doesn’t eat ice cream cones for lunch, nobody’s going to think it’s me.’ That was the thing that was sort of my most peculiar habit of the time,” Tarter recalls in this new video for PBS.
If you can think of all the media attention that surrounded the reboot of Cosmos, imagine that it’s 1997 and Contact has just been made into a movie. Tarter became a celebrity overnight, and describes the impact on her life. But she also explains why searching for life beyond Earth has relevance.
Tarter’s video is just one of several featured in the show “”The Secret Life of Scientists and Engineers.” To get the full story on Tarter’s links to Contact, check out this Universe Today story from 2012 where she reflected on the 15th anniversary of the movie.
Is there truly anything new under the Sun? Well, when it comes to amateur astronomy, many observers are branching out beyond the optical. And while it’s true that you can’t carry out infrared or X-ray astronomy from your backyard — or at least, not until amateurs begin launching their own space telescopes — you can join in the exciting world of amateur radio astronomy.
We’ll admit right out the gate that we’re a relative neophyte when it comes to the realm of radio astronomy. We have done radio observations of meteor showers in tandem with optical observations, and have delved into the trove of information on constructing radio telescopes over the years. Consider this post a primer of sorts, an intro into the world of radio amateur astronomy. If there’s enough interest, we’ll follow up with a multi-part saga, constructing and utilizing our own ad-hoc “redneck array” in our very own backyard with which to alarm the neighbors and probe the radio cosmos.
The “Itty-Bitty Array”- Re-purposing a TV Dish for amateur astronomy. Credit: NSF/NRAO/Assoc. Universities, Inc.
…And much like our exploits in planetary webcam imaging, we’ve discovered that you may have gear kicking around in the form of an old TV dish – remember satellite TV? – in your very own backyard. A simple radio telescope setup need not consist of anything more sophisticated than a dish (receiver), a signal strength detector (often standard for pointing a dish at a satellite during traditional installation) and a recorder. As you get into radio astronomy, you’ll want to include such essentials as mixers, oscillators, and amplifiers to boost your signal.
Frequency is the name of the game in amateur radio astronomy, and most scopes are geared towards the 18 megahertz to 10,000 megahertz range. A program known as Radio-SkyPipe makes a good graphic interface to turn your laptop into a recorder.
Radio astronomy was born in 1931, when Karl Jansky began researching the source of a faint background radio hiss with his dipole array while working for Bell Telephone. Jansky noticed the signal strength corresponded to the passage of the sidereal day, and correctly deduced that it was coming from the core of our Milky Way Galaxy located in the constellation Sagittarius. Just over a decade later, Australian radio astronomer Ruby Payne-Scott pioneered solar radio astronomy at the end of World War II, making the first ever observations of Type I and III solar bursts as well as conducting the first radio interferometry observations.
A replica of Jansky’s first steerable antenna at Green Bank, West Virginia. (Public Domain image)
What possible targets exist for the radio amateur astronomer? Well, just like those astronomers of yore, you’ll be able to detect the Sun, the Milky Way Galaxy, Geostationary and geosynchronous communication satellites and more. The simple dish system described above can also detect temperature changes on the surface of the Moon as it passes through its phases. Jupiter is also a fairly bright radio target for amateurs as well.
Radio meteors are also within the reach of your FM dial. If you’ve ever had your car radio on during a thunderstorm, you’ve probably heard the crackle across the radio spectrum caused by a nearby stroke of lightning. A directional antenna is preferred, but even a decent portable FM radio will pick up meteors on vacant bands outdoors. These are often heard as ‘pings’ or temporary reflections of distant radio stations off of the trail of ionized gas left in the wake of a meteor. Like with visual observing, radio meteors peak in activity towards local sunrise as the observer is being rotated forward into the Earth’s orbit.
Amateur SETI is also taking off, and no, we’re not talking about your crazy uncle who sits out at the end of runways watching for UFOs. BAMBI is a serious amateur-led project. Robert Gray chronicled his hunt for the elusive Wow! signal in his book by the same name, and continues an ad hoc SETI campaign. With increasingly more complex rigs and lots of time on their hands, it’s not out of the question that an amateur SETI detection could be achieved.
Another exciting possibility in radio astronomy is tracking satellites. HAM radio operators are able to listen in on the ISS on FM frequencies (click here for a list of uplink and downlink frequencies), and have even communicated with the ISS on occasion. AMSAT-UK maintains a great site that chronicles the world of amateur radio satellite tracking.
Amateur radio equipment that eventually made its way to to ISS aboard STS-106. (Credit: NASA).
Old TV dishes are being procured for professional use as well. One team in South Africa did just that back in 2011, scouring the continent for old defunct telecommunications dished to turn them into a low cost but effective radio array.
Several student projects exist out there as well. One fine example is NASA’s Radio JOVE project, which seeks student amateur radio observations of Jupiter and the Sun. A complete Radio Jove Kit, to include receiver and Radio-SkyPipe and Radio-Jupiter Pro software can be had for just under 300$ USD. You’d have a tough time putting together a high quality radio telescope for less than that! And that’s just in time for prime Jupiter observing as the giant planet approaches quadrature on April 1st (no fooling, we swear) and is favorably placed for evening observing, both radio and optical.
Fearing what the local homeowner’s association will say when you deploy your very own version of Jodrell Bank in your backyard? There are several online radio astronomy projects to engage in as well. SETI@Home is the original crowd sourced search for ET online. The Zooniverse now hosts Radio Galaxy Zoo, hunting for erupting black holes in data provided by the Karl Jansky Very Large Array and the Australia Telescope Compact Array. PULSE@Parkes is another exciting student opportunity that lets users control an actual professional telescope. Or you can just listen for meteor pings online via NASA’s forward scatter meteor radar based out of the Marshall Space Flight Center in Huntsville, Alabama. Adrian West also hosts live radio meteor tracking on his outstanding Meteorwatch website during times of peak activity.
A diagram of a basic forward scatter radar system for meteor observing. Credit: NASA
Interested? Other possibilities exist for the advanced user, including monitoring radio aurorae, interferometry, catching the hiss of the cosmic microwave background and even receiving signals from more distant spacecraft, such as China’s Yutu rover on the Moon.
Think of this post as a primer to the exciting world of amateur radio astronomy. If there’s enough interest, we’ll do a follow up “how-to” article as we assemble and operate a functional amateur radio telescope. Or perhaps you’re an accomplished amateur radio astronomer, with some tips and tricks to share. There’s more to the universe than meets the eye!
Researchers at NASA’s Goddard Spaceflight Center and the Massachusetts Institute of Technology have identified a fascinating natural process by which the magnetosphere of our fair planet can — to use a sports analogy — “shot block,” or at least partially buffer an incoming solar event.
The study, released today in Science Express and titled “Feedback of the Magnetosphere” describes new process discovered in which our planet protects the near-Earth environment from the fluctuating effects of inbound space weather.
Our planet’s magnetic field, or magnetosphere, spans our world from the Earth’s core out into space. This sheath typically acts as a shield. We can be thankful that we inhabit a world with a robust magnetic field, unlike the other rocky planets in the inner solar system.
But when a magnetic reconnection event occurs, our magnetosphere merges with the magnetic field of the Sun, letting in powerful electric currents that wreak havoc.
Now, researchers from NASA and MIT have used ground and space-based assets to identify a process that buffers the magnetosphere, often keeping incoming solar energy at bay.
The results came from NASA’s Time History Events and Macroscale Interactions during Substorms (THEMIS) constellation of spacecraft and was backed up by data gathered over the past decade for MIT’s Haystack Observatory.
Observations confirm the existence of low-energy plasma plumes that travel along magnetic field lines, rising tens of thousands of kilometres above the Earth’s surface to meet incoming solar energy at a “merging point.”
“The Earth’s magnetic field protects life on the surface from the full impact of these solar outbursts,” said associate director of MIT’s Haystack Observatory John Foster in the recent press release. “Reconnection strips away some of our magnetic shield and lets energy leak in, giving us large, violent storms. These plasmas get pulled into space and slow down the reconnection process, so the impact of the Sun on the Earth is less violent.”
The study also utilized an interesting technique known as GPS Total Electron Content or GPS-TEC. This ground-based technique analyzes satellite transmitted GPS transmissions to thousands of ground based receivers, looking for tell-tale distortions that that signify clumps of moving plasma particles. This paints a two dimensional picture of atmospheric plasma activity, which can be extended into three dimensions using space based information gathered by THEMIS.
And scientists got their chance to put this network to the test during the moderate solar outburst of January 2013. Researchers realized that three of the THEMIS spacecraft were positioned at points in the magnetosphere that plasma plumes had been tracked along during ground-based observations. The spacecraft all observed the same cold dense plumes of rising plasma interacting with the incoming solar stream, matching predictions and verifying the technique.
Launched in 2007, THEMIS consists of five spacecraft used to study substorms in the Earth’s magnetosphere. The Haystack Observatory is an astronomical radio observatory founded in 1960 located just 45 kilometres northwest of Boston, Massachusetts.
How will this study influence future predictions of the impact that solar storms have on the Earth space weather environment?
“This study opens new doors for future predictions,” NASA Goddard researcher Brian Walsh told Universe Today. “The work validates that the signatures of the plume far away from the Earth measured by spacecraft match signatures in the Earth’s upper atmosphere made from the surface of the Earth. Although we might not always have spacecraft in exactly the correct position to measure one of these plumes, we have almost continuous coverage from ground-based monitors probing the upper atmosphere. Future studies can now use these signatures as a proxy for when the plume has reached the edge of our magnetic shield (known as the magnetopause) which will help us predict how large a geomagnetic storm will occur from a given explosion from the Sun when it reaches the Earth.”
The structure of Earth’s magnetosphere. Credit-NASA graphic in the Public Domain.
Understanding how these plasma plumes essentially hinder or throttle incoming energy during magnetic reconnection events, as well as the triggering or source mechanism for these plumes is vital.
“The source of these plumes is an extension of the upper atmosphere, a region that space physicists call the plasmasphere,” Mr. Walsh told Universe Today. “The particles that make the plume are actually with us almost all of the time, but they normally reside relatively close to the Earth. During a solar storm, a large electric field forms and causes the upper layers of the plasmasphere to be stripped away and are sent streaming sunward towards the boundary of our magnetic field. This stream of particles is the ‘plume’ or ‘tail’”
Recognizing the impacts that these plumes have on space weather will lead to better predictions and forecasts for on- and off- the planet as well, including potential impacts on astronauts aboard the International Space Station. Flights over the poles are also periodically rerouted towards lower latitudes during geomagnetic storms.
“This study defines new tools for the toolbox we use to predict how large or how dangerous a given solar eruption will be for astronauts and satellites,” Walsh said. “This work offers valuable new insights and we hope these tools will improve prediction capabilities in the near future.”
And speaking of which, there’s a common misconception out there that we see reported every time auroral activity makes the news… remember that aurorae aren’t actually caused by solar wind particles colliding with our atmosphere, but the acceleration of particles trapped in our magnetic field fueled by the solar wind.
And speaking of solar activity, there’s also an ongoing controversy in the world of solar heliophysics as to the lackluster solar maximum for this cycle, and what it means for concurrent cycles #25 and #26.
It’s exciting times indeed in the science of space weather forecasting…
and hey, we got to drop in sports analogy, a rarity in science writing!
Starbursts in M82 as seen as radio frequencies from the by the Karl G. Jansky Very Large Array. Credit: Josh Marvil (NM Tech/NRAO), Bill Saxton (NRAO/AUI/NSF), NASA
Radio light, radio bright: when you look at M82 in this frequency range, a whole lot of activity pops out. The “Cigar Galaxy” is just 12 million light-years away from Earth and these days, is best known for hosting a supernova or star explosion so bright that amateurs can spot it in a small telescope.
Take a big radio telescope and peer at the galaxy’s center, and a violent picture emerges. Bright star nurseries and supernova leftovers are visible in this image from the Karl G. Jansky Very Large Array (the scientists can tell those apart using other data from the telescope.)
“The radio emission seen here is produced by ionized gas and by fast-moving electrons interacting with the interstellar magnetic field,” the National Radio Astronomy Observatory stated.
Most intriguing to scientists in this picture are the streamers of material in this area of M82, which is about 5,200 light-years across in the pictured central region. These previously undetected “wispy features” could be related to “superwind” coming from all this stellar activity, but scientists are still examining the link.
By the way, Supernova SN 2014J is not visible in this image because it is not active in radio waves. You can check out optical pictures of it, however, at this past Universe Today story.
The spiral galaxy NGC 6946 and its smaller companions are found to be surrounded by "cold rivers" of hydrogen
What happens when a galaxy doesn’t have enough hydrogen to support its stellar production process? Why, it sucks it from its hapless neighbors like some sort of cosmic vampire, that’s what. And evidence of this predatory process is what’s recently been observed with the National Science Foundation’s Robert C. Byrd Green Bank Telescope (GBT) in West Virginia, in the form of faint “cold flows” bridging intergalactic space between the galaxy NGC 6946 and its smaller companions.
“We knew that the fuel for star formation had to come from somewhere,” said astronomer D.J. Pisano from West Virginia University, author of the study. “So far, however, we’ve detected only about 10 percent of what would be necessary to explain what we observe in many galaxies. 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.”
NGC 6946 also goes by the festive moniker of “the Fireworks Galaxy,” due to the large amount of supernovae that have been observed within its arms — eight within the past century alone. Located 22 million light-years away between the constellations Cepheus and Cygnus, NGC 6946’s high rate of star formation has made astronomers curious as to how it (and other starburst galaxies like it) gets its stellar fuel.
One long-standing hypothesis is that large galaxies like NGC 6946 receive a constant supply of hydrogen gas by drawing it off their less-massive companions.
Chandra and Gemini image of NGC 6946 (X-ray: NASA/CXC/MSSL/R.Soria et al, Optical: AURA/Gemini OBs)
Now, thanks to the GBT’s unique capabilities — such as its immense single dish, unblocked aperture, and location in the National Radio Quiet Zone — direct observations have been made of the extremely faint radio emissions coming from neutral hydrogen flows connecting NGC 6946 with its smaller satellite galaxies.
According to a press release from the National Radio Astronomy Observatory:
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.
Another possible source of the cold flow is a previous collision with another galaxy, possibly even one of its own satellites, which would have left strands of atomic hydrogen in its wake. But if that were the case stars would likely have since formed within the filaments themselves, which has not yet been observed.
Image 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
