Space and astronomy news
What’s it like to spend a night at a huge telescope observatory? Jordi Busque recorded a brilliant timelapse of the Very Large Telescope (VLT) and the Atacama Large Millimeter/submillimeter Array (ALMA). What makes this video unique is not only the exotic location in Chile, but the use of sound in the area rather than music.
Continue reading “Amazing Video Timelapse Of Big Telescopes At Work In Chile”
It’s an engaging thought experiment.
What if Earth had multiple moons? Our world has one large natural satellite, just over a quarter the diameter, 1/50th the volume, and less than 1/80th the mass of our fair world. In fact, the Earth-Moon system has sometimes been referred to as a “binary planet,” and our Moon stands as the largest natural satellite of any planet — that is, if you subscribe to bouncing Pluto and Charon out of “the club” — in contrast to its primary of any moon in our solar system.
But what if we had two or more moons? And are there any tiny “moonlet” candidates lurking out there, awaiting discovery and perhaps exploration?
While historical searches for tiny secondary moons of the Earth — and even “moons of our Moon” — have turned up naught, the Earth does indeed capture asteroids as temporary moons and eject them back into solar orbit from time to time.
Now, a recent paper out of the University of Hawaii written in partnership with the SETI Institute and the Department of Physics at the University of Helsinki has looked at the possible prospects for the population of captured Near-Earth asteroids, and the feasibility of detecting these with existing and future systems about to come online.
The hunt for spurious moons of the Earth has a fascinating and largely untold history. Arthur Upgren’s outstanding book Many Skies devotes an entire chapter to the possible ramifications of an Earth with multiple moons… sure, more moons would be a bane for astrophotographers, but hey, eclipses and transits of the Sun would be more common, a definite plus.
In 1846, astronomer Frederic Petit announced the discovery of a tiny Earth-orbiting moon from Toulouse observatory. “Petit’s Moon” was said to orbit the Earth once every 2 hours and 44 minutes and reach an apogee of 3,570 kilometres and a perigee of just 11.4 (!) kilometres, placing it well inside the Earth’s atmosphere on closest approach.
A slightly more believable claim came from astronomer Georg Waltemath in 1898 for a moon 700 kilometres in size — he claimed it was, of course, a very dark body and not very easily visible — orbiting the Earth at about 2.5 times the distance of the Moon. Waltemath even made an announcement of his discovery, and claimed to have found a third moon of the Earth for good measure.
And a much more dubious claim came from the astrologer Walter Gornold in 1918 of a secondary moon, dubbed Lilith. Apparently, then (as now) astrologers never actually bothered to look at the skies…
Turns out, our large Moon makes a pretty good goaltender, ejecting —and sometimes taking a beating from — any tiny second moon hopeful. Of course, you can’t blame those astronomers of yore entirely. Though none of these spurious moons survived the test of observational verification, these discoveries often stemmed from early efforts to accurately predict the precise motion of the Moon. Astronomers therefore felt they were on the right track, looking for an unseen perturbing body.
Fast forward to the 21st century. Quasi-moons of the Earth, such as 3753 Cruithne, have horseshoe-shaped orbits and seem to approach and recede from our planet as both orbit the Sun. Similar quasi-moons of Venus have also been discovered.
And even returning space junk can masquerade as a moon of Earth, as was the case of J002E3 and 2010 QW1, which turned out to be boosters from Apollo 12 and the Chinese Chang’e-2 missions, respectively.
What modern researchers are looking for are termed Temporarily Captured Orbiters, or TCOs. The study notes that perhaps an average of a few dozen asteroids up to 1 to 2 metres in size are in a “steady state” population that may be orbiting the Earth at any given time on an enter, orbit, and eject sort of conveyor belt. Estimates suggest that a large 5 to 10 metre asteroid is captured every decade so, and a 100 metre or larger TCO is temporarily captured by the Earth every 100,000 years. The study also estimates that about 1% occasionally hit the Earth. And though it wasn’t a TCO, the ability to detect an Earthbound asteroid before impact was demonstrated in 2008 with the discovery of 2008 TC3, less than 24 hours prior to striking in the Sudanese desert.
“There are currently no projects that are solely looking for minimoons at this time,” lead researcher Bryce Bolin of the University of Hawaii told Universe Today. “There are several surveys, such as PanSTARRS, the Catalina Sky Survey and the Palomar Transit Factory that are currently in operation that have the capability of discovering minimoons.”
We’re getting better at this hazardous asteroid detection business, that’s for sure. The researchers modeled paths and orbits for TCOs in the study, and also noted that collections may “clump” at the anti-sunward L2 opposition point, and the L1 sunward point, with smaller distributions located at the east and west quadrature points located 90 degrees on either side of the Earth. The L2 point in particular might make a good place to start the search.
Ironically, systems such as LINEAR and PanSTARRS may have already captured a TCO in their data and disregarded them in their quest for traditional Near Earth Objects.
“Surveys such as PanSTARRS/LINEAR utilize a filtration process to remove artifacts and false positives in the data as it gets processed through the data pipeline,” Researcher Bryce Bolin told Universe Today. “A common method is to apply a rate of motion cut… this is effective in eliminating many artifacts (which) tend to have a rate of motion as measured by the pipeline which is very high.”
Such systems aren’t always looking for fast movers near Earth orbit that can produce a trail or streak which may reassemble space junk or become lost in the gaps over multiple detection devices. And speaking of which, researchers note that Arecibo and the U.S. Air Force’s Space Surveillance System may be recruited in this effort as well. To date, one definite TCO, named 2006 RH120 has been documented orbiting and departing from the vicinity of the Earth, and such worldlets might make enticing targets for future manned missions due to their relatively low Delta-V for arrival and departure.
PanSTARRS-2 saw first light last year in 2013, and is slated to go online for full science operations by the end of 2014. Eventually, the PanSTARRS system will employ four telescopes, and may find a bevy of TCOs. The researchers estimate in the study that a telescope such as Subaru stands a 90% chance of nabbing a TCO after only five nights of dedicated sweeps of the sky.
Finally, the study also notes that evidence miniature moonlets orbiting Earth may lurk in the all sky data gathered by automated cameras and amateur observers during meteor showers. Of course, we’re talking tiny, dust-to-pebble sized evidence, but there’s no lower limit as to what constitutes a moon…
And so, although moons such a “Lilith” and “Petit’s Moon” belong to the annuals of astronomical history, temporary “minimoons” of Earth are modern realities. And as events such as Chelyabinsk remind us, it’s always worthwhile to hunt for hazardous NEOs (and TCOs) that may be headed our way. Hey, to paraphrase science fiction author Larry Niven: unlike the dinosaurs, we have a space program!
Read more about the fascinating history of moons that never were and more in the classic book The Haunted Observatory.
Check it out. Look southwest at dusk tonight and you’ll see three of the solar system’s coolest personalities gathering for a late dinner. Saturn, Mars and the waxing crescent moon will sup in Libra ahead of the fiery red star Antares in Scorpius. All together, a wonderful display of out-of-this-world worlds.
If you have binoculars, take a closer look at the thick lunar crescent. Several prominent lunar seas, visible to the naked eye as dark patches, show up more clearly and have distinctly different outlines even at minimal magnification. Each is a plain of once-molten lava that oozed from cracks in the moon’s crust after major asteroid strikes 3-3.5 billion years ago.
Larger craters also come into view at 10x including the remarkable trio of Theophilus, Cyrillus and Catharina, each of which spans about 60 miles (96 km) across. Even in 3-inch telescope, you’ll see that Theophilus partly overlaps Cyrillus, a clear indicator that the impact that excavated the crater happened after Cyrillus formed.
Notice that the rim Theophilus crater is still relatively crisp and fresh compared to the older, more battered outlines of its neighbors. Yet another sign of its relative youth.
Astronomers count craters on moons and planets to arrive at relative ages of their surfaces. Few craters indicate a youthful landscape, while many overlapping ones point to an ancient terrain little changed since the days when asteroids bombarded all the newly forming planets and moons. Once samples of the moon were returned from the Apollo missions and age-dated, scientists could then assign absolute ages to particular landforms. When it comes to planets like Mars, crater counts are combined with estimates of a landscape’s age along with information about the rate of impact cratering over the history of the solar system. Although we have a number of Martian meteorites with well-determined ages, we don’t know from where on Mars they originated.
Another crater visible in 10x binoculars tonight is Maurolycus (more-oh-LYE-kus), a great depression 71 miles (114 km) across located in the moon’s southern hemisphere in a region rich with overlapping craters. Low-angled sunlight highlighting the crater’s rim will make it pop near the moon’s terminator, the dividing line between lunar day and night.
Like Theophilus, Maurolycus overlaps a more ancient, unnamed crater best seen in a small telescope. Notice that Maurolycus is no spring chicken either; its floor bears the scares of more recent impacts.
Putting it all into context, despite their varying relative ages, most of the moon’s craters are ancient, punched out by asteroid and comet bombardment more than 3.8 billion years ago. To look at the moon is to see a fossil record of a time when the solar system was a terrifyingly untidy place. Asteroids beat down incessantly on the young planets and moons.
Despite the occasional asteroid scare and meteorite fall, we live in relative peace now. Think what early life had to endure to survive to the present. Deep inside, our DNA still connects us to the terror of that time.
Now that’s pure gorgeous. As Comet C/2013 A1 Siding Spring sidles towards its October 19th encounter with Mars, it’s passing a trio of sumptuous deep sky objects near the south celestial pole this week. Astrophotographers weren’t going to let the comet’s picturesque alignments pass without notice. Rolando Ligustri captured this remarkable view using a remote, computer-controlled telescope on August 29th. It shows the rich assemblage of stars and star clusters that comprise the Small Magellanic Cloud, one of the Milky Way’s satellite galaxies located 200,000 light years away.
Looking like a fuzzy caterpillar, Siding Spring seems to crawl between the little globular cluster NGC 362 and the rich swarm called 47 Tucanae, one of the few globulars bright enough to see with the naked eye. C/2013 A1 is currently circumpolar from many locations south of the equator and visible all night long. Glowing at around magnitude +9.5 with a small coma and brighter nucleus, a 6-inch or larger telescope will coax it from a dark sky. Siding Spring dips farthest south on September 2-3 (Dec. -74º) and then zooms northward for Scorpius and Sagittarius. It will encounter additional deep sky objects along the way, most notably the bright open cluster M7 on October 5-6, before passing some 82,000 miles from Mars on October 19th.
While the chance of a Mars impact is near zero, the fluffy comet’s fluffy coma and broad tail, both replete with tiny but fast-moving (~125,000 mph) dust particles, might pose a hazard for spacecraft orbiting the Red Planet. Assuming either coma or tail grows broad enough to sweep across the Martian atmosphere, impacting dust might create a spectacular meteor shower. Mars Rover cameras may be used to photograph the comet before the flyby and to capture meteors during its closest approach. NASA plans to ‘hide’ its orbiting probes on the opposite side of the planet for a brief time during the approximately 4-hour-long encounter just in case.
Today, Siding Spring’s coma or temporary atmosphere measures about 12,000 miles (19,300 km) wide. While I can’t get my hands on current dust production rates, in late January, when it was farther from the sun than at present, C/2013 A1 kicked out ~800,000 lbs per hour (~100 kg/sec). On October 19th, observers across much of the globe with 6-inch or larger instruments will witness the historic encounter with their own eyes at dusk in the constellation Sagittarius.
Fall will soon be at our doorstep. But before the leaves change colors and the smell of pumpkin fills our coffee shops, the Pleiades star cluster will mark the new season with its earlier presence in the night sky.
The delicate grouping of blue stars has been a prominent sight since antiquity. But in recent years, the cluster has also been the subject of an intense debate, marking a controversy that has troubled astronomers for more than a decade.
Now, a new measurement argues that the distance to the Pleiades star cluster measured by ESA’s Hipparcos satellite is decidedly wrong and that previous measurements from ground-based telescopes had it right all along.
The Pleiades star cluster is a perfect laboratory to study stellar evolution. Born from the same cloud of gas, all stars exhibit nearly identical ages and compositions, but vary in their mass. Accurate models, however, depend greatly on distance. So it’s critical that astronomers know the cluster’s distance precisely.
A well pinned down distance is also a perfect stepping stone in the cosmic distance ladder. In other words, accurate distances to the Pleiades will help produce accurate distances to the farthest galaxies.
But accurately measuring the vast distances in space is tricky. A star’s trigonometric parallax — its tiny apparent shift against background stars caused by our moving vantage point — tells its distance more truly than any other method.
Originally the consensus was that the Pleiades are about 435 light-years from Earth. However, ESA’s Hipparcos satellite, launched in 1989 to precisely measure the positions and distances of thousands of stars using parallax, produced a distance measurement of only about 392 light-years, with an error of less than 1%.
“That may not seem like a huge difference, but, in order to fit the physical characteristics of the Pleiades stars, it challenged our general understanding of how stars form and evolve,” said lead author Carl Melis, of the University of California, San Diego, in a press release. “To fit the Hipparcos distance measurement, some astronomers even suggested that some type of new and unknown physics had to be at work in such young stars.”
If the cluster really was 10% closer than everyone had thought, then the stars must be intrinsically dimmer than stellar models suggested. A debate ensued as to whether the spacecraft or the models were at fault.
To solve the discrepancy, Melis and his colleagues used a new technique known as very-long-baseline radio interferometry. By linking distant telescopes together, astronomers generate a virtual telescope, with a data-gathering surface as large as the distances between the telescopes.
The network included the Very Long Baseline Array (a system of 10 radio telescopes ranging from Hawaii to the Virgin Islands), the Green Bank Telescope in West Virginia, the William E. Gordon Telescope at the Arecibo Observatory in Puerto Rico, and the Effelsberg Radio Telescope in Germany.
“Using these telescopes working together, we had the equivalent of a telescope the size of the Earth,” said Amy Miouduszewski, of the National Radio Astronomy Observatory (NRAO). “That gave us the ability to make extremely accurate position measurements — the equivalent of measuring the thickness of a quarter in Los Angeles as seen from New York.”
After a year and a half of observations, the team determined a distance of 444.0 light-years to within 1% — matching the results from previous ground-based observations and not the Hipparcos satellite.
“The question now is what happened to Hipparcos?” Melis said.
The spacecraft measured the position of roughly 120,000 nearby stars and — in principle — calculated distances that were far more precise than possible with ground-based telescopes. If this result holds up, astronomers will grapple with why the Hipparcos observations misjudged the distances so badly.
ESA’s long-awaited Gaia observatory, which launched on Dec. 19, 2013, will use similar technology to measure the distances of about one billion stars. Although it’s now ready to begin its science mission, the mission team will have to take special care, utilizing the work of ground-based radio telescopes in order to ensure their measurements are accurate.
The findings have been published in the Aug. 29 issue of Science and is available online.
Never seen Neptune? Now is a good time to try, as the outermost ice giant world reaches opposition this weekend at 14:00 Universal Time (UT) or 10:00 AM EDT on Friday, August 29th. This means that the distant world lies “opposite” to the Sun as seen from our Earthly perspective and rises to the east as the Sun sets to the west, riding high in the sky across the local meridian near midnight.
2014 finds Neptune shining at magnitude +7.6 in the constellation of Aquarius. Unfortunately, the planet is too faint to be seen with the naked eye, but can be sighted using a good pair of binoculars if know exactly where to look for it. Though the telescope, Neptune exhibits a tiny blue-gray disk 2.4” across — 750 “Neptunes” would fit across the apparent diameter of the Full Moon — that’s barely discernible. Don’t be afraid to crank up the magnification in your quest. We’ve found Neptune on years previous by patently examining suspect stars one by one, looking for the one in the field that stubbornly refuses to focus to a star-like point. Make sure your optics are well collimated to attempt this trick. Neptune will exhibit a tiny fuzzy disk, much like a second-rate planetary nebula. In fact, this is where “planetaries” get their moniker, as the pesky deep sky objects resembled planets in those telescopes of yore…
The 1846 discovery of Neptune stood as a vindication of the (then) new-fangled theory of Newtonian gravitational dynamics. Uranus was discovered just decades before by Sir William Hershel in 1781, and it stubbornly refused to follow predictions concerning its position. French astronomer Urbain Le Verrier correctly assumed that an unseen body was tugging on Uranus, predicted the position of the suspect object in the sky, and the race was on. On the night of September 24th, Heinrich Louis d’Arrest and Johann Gottfried Galle observing from the Berlin observatory became the first humans to gaze upon the new world referring to it as such. Did you know: Galileo actually sketched Neptune near Jupiter in 1612? And those early 18th century astronomers got a lucky break… had Neptune happened to have been opposite to Uranus in its orbit, it might’ve eluded discovery for decades to come!
It’s also sobering to think that Neptune has only recently completed a single orbit of the Sun in 2011 since its discovery. Opposition of Neptune occurs once every 368 days, meaning that opposition is slowly moving forward by about three days a year on our Gregorian calendar and will soon start occurring in northern hemisphere Fall.
Now for the “wow factor” of what you’re actually seeing. Though tiny, Neptune is actually 24,622 kilometres in radius, and is 58 times as big as the Earth in volume and over 17 times as massive. Neptune is 29 A.U.s or 4.3 billion kilometres from Earth at opposition, meaning the light we see took almost four hours to transit from Neptune to your backyard.
Neptune is currently south of the equator, and won’t be north of it again until 2027.
Next month, keep an eye on Neptune as it passes less than half a degree north of the +4.8 magnitude star Sigma Aquarii through mid-September, making a great guide to find the planet…
Still not enough of a challenge? Try tracking down Neptune’s large moon, Triton. Orbiting the planet in a retrograde path once every 5.9 days, Triton is within reach of a large backyard scope at magnitude +14. Triton never strays more than 15” from the disk of Neptune, but opposition is a great time to cross this curious moon off of your observing life list. Neptune has 14 moons at last count.
And speaking of Triton, NASA recently released a new map of the moon. We’ve only gotten one good look at Triton, Neptune, and its retinue of moons back in 1989 when Voyager 2 conducted the only flyby of the planet to date. Will Pluto turn out to be Triton’s twin when New Horizons completes its historic flyby next summer?
The Moon also passes 4.3 degrees north of Neptune on September 8th on its way to “Supermoon 3 of 3” for 2014 on the night of September 8th/9th. Fun fact: a cycle of occultations of Neptune by the Moon commences on June 2016.
When will we explore Neptune once more? Will a dedicated “Neptune orbiter” ever make its way to the planet in our lifetimes? All fun things to ponder as you check out the first planet discovered using scientific reasoning this weekend.
Stars and planets form out of vast clouds of dust and gas. Small pockets in these clouds collapse under the pull of gravity. But as the pocket shrinks, it spins rapidly, with the outer region flattening into a disk.
Eventually the central pocket collapses enough that its high temperature and density allows it to ignite nuclear fusion, while in the turbulent disk, microscopic bits of dust glob together to form planets. Theories predict that a typical dust grain is similar in size to fine soot or sand.
In recent years, however, millimeter-size dust grains — 100 to 1,000 times larger than the dust grains expected — have been spotted around a few select stars and brown dwarfs, suggesting that these particles may be more abundant than previous thought. Now, observations of the Orion nebula show a new object that may also be brimming with these pebble-size grains.
The team used the National Science Foundation’s Green Bank Telescope to observe the northern portion of the Orion Molecular Cloud Complex, a star-forming region that spans hundreds of light-years. It contains long, dust-rich filaments, which are dotted with many dense cores. Some of the cores are just starting to coalesce, while others have already begun to form protostars.
Based on previous observations from the IRAM 30-meter radio telescope in Spain, the team expected to find a particular brightness to the dust emission. Instead, they found that it was much brighter.
“This means that the material in this region has different properties than would be expected for normal interstellar dust,” said Scott Schnee, from the National Radio Astronomy Observatory, in a press release. “In particular, since the particles are more efficient than expected at emitting at millimeter wavelengths, the grains are very likely to be at least a millimeter, and possibly as large as a centimeter across, or roughly the size of a small Lego-style building block.”
Such massive dust grains are hard to explain in any environment.
Around a star or a brown dwarf, it’s expected that drag forces cause large particles to lose kinetic energy and spiral in toward the star. This process should be relatively fast, but since planets are fairly common, many astronomers have put forth theories to explain how dust hangs around long enough to form planets. One such theory is the so-called dust trap: a mechanism that herds together large grains, keeping them from spiraling inward.
But these dust particles occur in a rather different environment. So the researchers propose two new intriguing theories for their origin.
The first is that the filaments themselves helped the dust grow to such colossal proportions. These regions, compared to molecular clouds in general, have lower temperatures, high densities, and lower velocities — all of which encourage grain growth.
The second is that the rocky particles originally grew inside a previous generation of cores or even protoplanetary disks. The material then escaped back into the surrounding molecular cloud.
This finding further challenges theories of how rocky, Earth-like planets form, suggesting that millimeter-size dust grains may jump-start planet formation and cause rocky planets to be much more common than previously thought.
The paper has been accepted for publication in the Monthly Notices of the Royal Astronomical Society.
Astronomers have spotted, for the first time, a dense galactic core blazing with the light of millions of newborn stars in the early universe.
The finding sheds light on how elliptical galaxies, the large, gas-poor gatherings of older stars, may have first formed in the early universe. It’s a question that has eluded astronomers for decades.
The research team first uncovered the compact galactic core, dubbed GOODS-N-774, in images from the Hubble Space Telescope. Later observations from the Spitzer Space Telescope, the Herschel Space Observatory, and the W.M. Keck Observatory helped make this a true scientific finding.
The core formed 11 billion years ago, when the universe was less than 3 billion years old. Although only a fraction of the size of the Milky Way, at that time it already contained above twice as many stars as our own galaxy.
Theoretical simulations suggest that giant elliptical galaxies form from the inside out, with a large core marking the very first stages of formation. But most searches for these forming cores have come up empty handed, making this a first observation and a phenomenal find.
“We really hadn’t seen a formation process that could create things that are this dense,” explained lead author Erica Nelson from Yale University in a press release. “We suspect that this core-formation process is a phenomenon unique to the early universe because the early universe, as a whole, was more compact. Today, the universe is so diffuse that it cannot create such objects anymore.”
Alongside determining the galaxy’s size from the Hubble images, the team dug into archived far-infrared images from Spitzer and Herschel to calculate how fast the compact galaxy is creating stars. It seems to be producing 300 stars per year, a rate 30 times greater than the Milky Way.
The frenzied star formation likely occurs because the galactic core is forming deep inside a gravitational well of dark matter. Its unusually high mass constantly pulls gas in, compressing it and sparking star formation.
But these bursts of star formation create dust, which blocks the visible light. This helps explain why astronomers haven’t seen such a distant core before, as they may have been easily missed in previous surveys.
The team thinks that shortly after the early time period we can see, the core stopped forming stars. It likely then merged with other smaller galaxies, until it transformed into a much greater galaxy, similar to the more massive and sedate elliptical galaxies we see today.
“I think our discovery settles the question of whether this mode of building galaxies actually happened or not,” said coauthor Pieter van Dokkum from Yale University. “The question now is, how often did this occur?”
The team suspects that other galactic cores are abundant, but hidden behind their own dust. Future infrared telescopes, such as the James Webb Space Telescope, should be able to find more of these early objects.
The paper was published Aug. 27 in Nature and is available online.
Most scientists can see, hear, smell, touch or even taste their research. But astronomers can only study light — photons traveling billions of light-years across the cosmos before getting scooped up by an array of radio dishes or a single parabolic mirror orbiting the Earth.
Luckily the universe is overflowing with photons across a spectrum of energies and wavelengths. But astronomers don’t fully understand where most of the light, especially in the early universe, originates.
Now, new simulations hope to uncover the origin of the ultraviolet light that bathes — and shapes — the early cosmos.
“Which produces more light? A country’s biggest cities or its many tiny towns?” asked lead author Andrew Pontzen in a press release. “Cities are brighter, but towns are far more numerous. Understanding the balance would tell you something about the organization of the country. We’re posing a similar question about the universe: does ultraviolet light come from numerous but faint galaxies, or from a smaller number of quasars?”
Answering this question will give us a valuable insight into the way the universe built its galaxies over time. It will also help astronomers calibrate their measurements of dark energy, the mysterious agent that is somehow accelerating the universe’s expansion.
The problem is that most of intergalactic space is impossible to see directly. But quasars — brilliant galactic centers fueled by black holes rapidly accreting material — shine brightly and illuminate otherwise invisible matter. Any intervening gas will absorb the quasar’s light and leave dark lines in the arriving spectrum.
“Because they can be seen at such great distances, quasars are a useful probe for finding out the properties of the universe,” said Pontzen. “Distant quasars can be used as a backlight, and the properties of the gas between them and us are imprinted on the light.
Multiple clouds of intervening hydrogen gas leave a “forest” of hydrogen absorption lines in the quasar’s spectrum. But, crucially, not all gas in the universe contributes to these dark lines. When hydrogen is bombarded by ultraviolet light, it becomes ionized — the electron separates from the proton — which renders it transparent.
So the pattern of absorption lines visible in a quasar’s spectrum map out the location of neutral and ionized regions in between the quasar and the Earth.
This pattern will tell astronomers the main contributing light source in the early universe. Quasars are fairly limited in number but individually extremely bright. If they caused most of the radiation, the pattern will be far from uniform, with some areas nearly transparent and others strongly opaque. But if galaxies, which are far more numerous but much dimmer, caused most of the radiation, the pattern will be very uniform, with evenly spaced absorption lines.
Current samples of quasars aren’t quite big enough for a robust analysis of the subtle differences between the two scenarios. But Pontzen and colleagues show that a number of new surveys should shed light on the question.
The team is hopeful the DESI (Dark Energy Spectroscopic Instrument) survey, which will look at about a million distant quasars in order to better understand dark energy, will also show the distribution of intervening gas.
“It’s amazing how little is known about the objects that bathed the universe in ultraviolet radiation while galaxies assembled into their present form,” said coauthor Hiranya Peiris. “This technique gives us a novel handle on the intergalactic environment during this critical time in the Universe’s history.”
The paper was published Aug. 27 in the Astrophysical Journal Letters and is available online.
An international team of astronomers has obtained the best view yet of two galaxies colliding when the universe was only half its current age.
The team relied heavily on space- and ground-based telescopes, including the Hubble Space Telescope, the Atacama Large Millimeter/submillimeter Array (ALMA), the Keck Observatory, and the Karl Jansky Very Large Array (VLA). But the greatest asset was a chance cosmic alignment.
“While astronomers are often limited by the power of their telescopes, in some cases our ability to see detail is hugely boosted by natural lenses created by the universe,” said lead author Hugo Messias of the Universidad de Concepción in Chile and the Centro de Astronomia e Astrofísica da Universidade de Lisboa in Portugal.
Such a rare cosmic alignment plays visual tricks, where the intervening lens (be it a galaxy or a galaxy cluster) appears to bend and even magnify the distant light. This effect, called gravitational lensing, allows astronomers to study objects which would not be visible otherwise and to directly compare local galaxies with much more remote galaxies, seen when the universe was significantly younger.
The distant object in question, dubbed H-ATLAS J142935.3-002836, was originally spotted in the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS). Although very faint in visible light pictures, it is among the brightest gravitationally lensed objects in the far-infrared regime found so far.
The Hubble and Keck images reveal that the foreground galaxy is a spiral galaxy, seen edge-on. Although the galaxy’s large dust clouds obscure part of the background light, both ALMA and VLA can observe the sky at longer wavelengths, which are unaffected by dust.
Using the combined data, the team discovered that the background system was actually an ongoing collision between two galaxies.
First, the team noticed that these two galaxies resembled a much closer system: the Antennae galaxies, two galaxies that have spent the past few hundred million years in a whirling embrace as they merge together. The similarity suggested a collision, but ALMA — with its high sensitivity and spatial resolution — was able to verify it.
ALMA has the unique ability to detect the emission from carbon monoxide, as opposed to other telescopes, which might only be able to probe the absorption along the line of sight. This allowed astronomers to measure the velocity of the gas in the more distant object. With this information, they were able to show that the lensed galaxy is indeed an ongoing galactic collision.
Such collisions naturally enhance star formation. Any gas within the galaxies will feel a headwind, much as a runner feels a wind even on the stillest day, and become compressed enough to spark star formation. Sure enough, ALMA shows that the two galaxies are forming hundreds of new stars each year.
“ALMA enabled us to solve this conundrum because it gives us information about the velocity of the gas in the galaxies, which makes it possible to disentangle the various components, revealing the classic signature of a galaxy merger,” said ESO’s Director of Science and coauthor of the new study, Rob Ivison. “This beautiful study catches a galaxy merger red handed as it triggers an extreme starburst.”
The findings have been published in the Aug. 26 issue of Astronomy & Astrophysics and is available online.