Planets can exist in multiple-star systems. Astronomers have even observed them. Take Kepler-47c, a planet five times the mass of the Earth, in a very Earth-like orbit. The only difference is instead of one star in the center of the system, it has two. So contact your local travel agent and you can recreate that iconic film moment — just don’t forget a space suit: Kepler-47c isn’t exactly capable of supporting life, since it’s most likely a gas giant.
Astronomers don’t know for sure just how common planets are around multiple-star systems. To be fair, we don’t know for sure just how common planets are anywhere, but they appear to be just this side of quite numerous: a hundred billion planets, with a few billion of them life-friendly, in the Milky Way alone.
But you just can’t plop planets down wherever you feel like it, especially when it comes to multiple-star systems. The problem, as usual, is gravity.
Drawn into gravity
We usually think of gravity as easy. Two things attract each other. Done. Drop something, it falls. Launch a rocket, it doesn’t. Sure there are tides, and don’t get near black holes, but this is the kind of stuff that dead folks with interesting wigs figured out a long time ago.
Gravity is indeed pretty easy, when it’s just two things interacting. One planet plus one star? You’re golden. It’s so easy you can even write down the mathematical solutions of the possible orbits. All sorts of stable configurations. But put in another star? Or a third? The situation gets…tricky. Orbital stability isn’t a given. And the math? Just look up a picture of Henri Poincare, one of the first people to try to tackle the problem of multiple objects orbiting together. Look into his eyes, and tell me that isn’t the face of a man who has stared into the depths of mathematical hell and barely survived with his sanity intact.
I’m not saying that it’s impossible: You may have noticed, if you are observant enough, that our own solar system contains more than two objects. Our system didn’t fall apart billions of years ago because there’s a hierarchy. In other words, each planet or moon or asteroid or whatever is dominated by one and only one other player.
For example, the Earth cares a lot about the gravitational pull of the sun, but not of Jupiter, and Jupiter feels likewise. The moon cares a lot about the Earth, but not the sun or Ceres. And so on. Every interaction is essentially one-to-one. Thus, all the planets get nice stable little orbits that can last for billions of years. If you broke this hierarchy, say, by shoving Jupiter into the inner system, or inflating it to be 10 times more massive, its gravity would start to compete with the sun’s, the hierarchy would be broken, and so would the solar system.
All this gravity business means that planets around multiple star systems have only a few orbital options if they intend to stick around. Most potential orbits are unstable: even the faintest stellar breeze could potentially knock them either out of the system altogether or crashing into another body. To make a system a long-term home, a planet has two choices: either ensure that the gravitational pull of one star completely dominates the other, or that their gravitational effects are equal.
And that’s just for a binary star. Don’t get me started on multiples.
When two stars dance
Take Kepler-47c: the two stars orbit each other very closely and tightly , and the planet itself is rather far out. Far enough, in fact, that gravitywise the planet doesn’t even care that there’s two stars — to the planet, the center of the system just looks like a single star with the combined mass of the two suns. Stability achieved.
Another possible configuration is for a planet to only orbit a single star, with the other star far enough away and/or small enough to not matter. Figure-eight patterns around both stars are technically possible, but come on, don’t hold your breath looking for one. Truly chaotic orbits — stable, but never repeating the same pattern twice — would be extremely rare, too, as fun as they might be.
So we can get planets in a binary system, although they might be more rare than planets around solitary stars. But there are heaps of binary stars out there, so even if a tiny percentage of them host planets, that still leaves heaps of planets.
Life on around a binary-star system
What does this mean for such a planet’s weather and the prospects for life? That’s a little more difficult to say, since it’s hard to make general, broad-brush statements about the possibility of life anywhere, let alone in these kinds of binary systems. Instead, it’s best to examine each system (real or imagined) in detail.
While binary systems certainly have a habitable zone, where liquid water could potentially exist on the surface of a planet, life might find it difficult to gain a foothold. Orbiting two stars at once, as our friend Kepler-47c does, makes life very elliptical, occasionally bringing the planet out of the zone. Life doesn’t take too kindly to frequently freezing over.
Orbiting just one star in a binary system? Well, sometimes you’ll have two stars in your sky at once, which can be a tad toasty. And sometimes you’ll have a star on each face of the planet, ruining the night. And don’t forget the double-doses of UV radiation and solar flares.
With that kind of instability, erraticism and irradiation, it’s hard to imagine complex life evolving with the kind of regularity it needs. But thankfully, Mother Nature isn’t limited by our lack of imagination, so who knows what’s out there!
Learn more by listening to the episode “Is Life Possible Around a Binary Star?” on the Ask A Spaceman podcast, available on iTunes and on the Web at http://www.askaspaceman.com. Thanks to Adam Diener for the great question! Ask yours on Twitter using #AskASpaceman or by following @PaulMattSutter.
In the new image, researchers were able to make out the glow of ionized carbon (shown in red) in the process of assembling into a galaxy — called BDF 3299 — around 800 million years after the Big Bang. The carbon cloud is overlaid on another picture of the galaxy’s neighborhood, where you can tell the galaxy itself is off to the right. Researchers think that carbon’s glow is obscured by the supernova blasts and chaos of galactic formation there, but the cold store of carbon nearby still shines as the galaxy draws from it.
The image was captured by the Atacama Large Millimeter/submillimeter Array (ALMA), a giant radio telescope in Chile consisting of 66 radio antennas, most 40 feet (12 meters) in diameter.
“This is the most distant detection ever of this kind of emission from a ‘normal’ galaxy, seen less than one billion years after the Big Bang,” Andrea Ferrara, a cosmologist and co-author of the study from Scuola Normale Superiore, a part of the Pisa University System in Italy, said in a statement. “It gives us the opportunity to watch the build-up of the first galaxies. For the first time we are seeing early galaxies not merely as tiny blobs, but as objects with internal structure!”
BDF 3299 was among the first galaxies to condense out of cold matter during the galaxy’s reionization phase. Seeing the crooked galaxy’s formation offers a chance to refine models of the very early universe.
“We have been trying to understand the interstellar medium and the formation of the reionisation sources for many years,” Ferrara said. “Finally, to be able to test predictions and hypotheses on real data from ALMA is an exciting moment and opens up a new set of questions. This type of observation will clarify many of the thorny problems we have with the formation of the first stars and galaxies in the Universe.”
The black hole orbits in tandem with a sunlike star at the heart of the system V404 Cygni, which lies about 8,000 light-years from Earth. Swift spotted an outburst of activity from the black hole on June 15, and the spacecraft’s X-ray Telescope detected the expanding rings during observations made in late June and early July, NASA officials said.
The black hole is easy to see in the new images without the rings pointing the way; it appears as a bluish-white dot. But the bull’s-eye really marks the spot of the invisible interstellar dust between Earth and the system.
The various layers of dust, which are found between 4,000 and 7,000 light-years from Earth, reflect some of the X-rays over toward us as they fan out in all directions from the black hole.
“The flexible planning of Swift observations has given us the best dust-scattered X-ray ring images ever seen,” Andrew Beardmore, an astronomer at the University of Leicester in England and leader of the investigating team, said in a statement. “With these observations, we can make a detailed study of the normally invisible interstellar dust in the direction of the black hole.”
V404 Cygni’s arousal on June 15 was likely caused by material falling into the black hole, part of a cycle that repeats every few decades, researchers said. The companion star is about 10 percent as massive as the black hole, and the behemoth pulls a stream of gas away from it over time. The cool gas can resist the black hole’s pull, but when enough gas builds up and heats up, it’s suddenly pulled into the center of the black hole, triggering a sudden outburst of X-rays. Astronomers caught its most recent eruption before this one in 1989.
The outburst offers a rare opportunity to gather data about the nearby binary system, the black hole within it and the normally undetectable interstellar dust clouds that stand in its way, NASA officials said.
A newfound giant black hole nearly as massive as 7 billion suns is dozens of times larger than astronomers expected given its host galaxy’s size, researchers say.
This finding may call most current models of galaxy formation into question, scientists added.
Astronomers investigated a supermassive black hole known as CID-947 using the W.M. Keck Observatory in Hawaii, NASA’s Chandra X-ray Observatory and the European Space Agency’s XMM-Newton spacecraft.
This black hole, one of the largest ever seen, formed in the early universe about 11.7 billion years ago — 2 billion years after the Big Bang. The very fast motion of gas near the black hole suggests that it has a very high mass — the equivalent of about 7 billion suns.
The discovery was unexpected. “Our survey was designed to observe the average objects, not the exotic ones,” study co-author C. Megan Urry, of Yale University, said in a statement. “This project specifically targeted moderate black holes that inhabit typical galaxies today. It was quite a shock to see such a ginormous black hole.”
However, it was the mass of the galaxy surrounding this black hole that most surprised the research team.
“The measurements correspond to the mass of a typical galaxy,” study lead author Benny Trakhtenbrot, an astrophysicist at the Swiss Federal Institute of Technology in Zurich, said in a statement. “We therefore have a gigantic black hole within a normal-size galaxy.”
Most galaxies, including the Milky Way, possess at their hearts a supermassive black hole with a mass ranging from millions to billions of times the mass of the sun. The supermassive black holes seen up to now usually make up only 0.2 to 0.5 percent of the mass of their galaxies — far less than CID-947 does.
“The black hole has roughly one-tenth of the mass of the host,” Trakhtenbrot told Space.com. “The black hole is massive compared with the normal host galaxy.” The result was so surprising that the astronomers had outside experts verify their results independently.
Current models of galaxy formation suggest that galaxies and their supermassive black holes evolve in sync, growing at the same rate. However, CID-947 defies this rule, precociously growing much faster than researchers would have predicted.
“The black hole and the galaxy were not growing in parallel, as many models would suggest,” Trakhtenbrot said.
In addition, the scientists found that, although the black hole had reached the end of its growth, stars were still forming in its galaxy. Prior research suggested that radiation and flowing gas from around the black hole would stifle the birth of stars.
“The black hole didn’t affect the growth of the galaxy — again, contrary to many common models and ideas in the field,” Trakhtenbrot said. “The black hole has done most of its growth and is shutting down. The galaxy is still growing.”
This finding supports previous research suggesting that black holes may have grown incredibly rapidly in the newborn universe, Trakhtenbrot said. For instance, the early universe was much smaller, and thus denser, on average than it is today, which could have helped black holes back then gorge on “an almost continuous inflow of gas without ‘burping’ too much of it back into the galaxy,” Trakhtenbrot said.
Trakhtenbrot and his colleagues now want to analyze more similarly ancient supermassive black holes to learn more about their interplay with their galaxies.
After taking a 26-year nap, a waking black hole released a burst of X-rays that lit up astronomical observatories on June 15 — and it’s still making a ruckus today.
Astronomers identified the revived black hole as an “X-ray nova” — a sudden increase in star luminosity — coming from a binary system in the constellation Cygnus. The outburst may have been caused by material falling into a black hole.
The burst was first caught by NASA’s Swift satellite, and then by a Japanese experiment on the International Space Station, called Monitor of All-sky X-ray Image (MAXI). [Black Hole Wakes Up With A Bang (Video)]
“Relative to the lifetime of space observatories, these black-hole eruptions are quite rare,” Neil Gehrels, Swift’s principal investigator at NASA’s Goddard Space Flight Center, said in a statement. “So, when we see one of them flare up, we try to throw everything we have at it, monitoring across the spectrum, from radio waves to gamma-rays.”
The binary system responsible for the eruption is called V404 Cygni, according to the statement from NASA. It’s made up of a star slightly smaller than the sun that orbits a black hole 10 times its mass. The orbital period is just 6.5 days, which makes it more than 10 times faster than Mercury orbits our own sun, the statement said.
Because the star orbits so closely to the black hole, the massive body pulls a stream of gas away from the star. Over time, the gas forms into a disc around the black hole.
When the gas is cooler, it’s able to resist the black hole’s pull. But as more gas gathers and it warms, eventually, the dam bursts, and gas is pulled toward the black hole. The rapidly moving, hot gas radiates an outburst of X-rays as it falls toward the gaping black maw, according to NASA.
This stellar duo has been active before, but only sporadically. The system was caught fluctuating in visible light in 1938 and 1956, and then in X-rays in 1989. The latter outburst was observed by instruments aboard Russia’s Mir space station and a Japanese X-ray satellite called Ginga.
Since this most recent outburst began, V404 Cygni has fluctuated several times in brightness — sometimes up to 50 times brighter than the Crab Nebula, a very bright source in X-rays, said Erik Kuulkers, a project scientist for the European Space Agency’s INTEGRAL satellite, one of the satellites that is studying V4040 Cygni. It also has caused more than 70 “triggers” of the burst monitor on NASA’s Fermi Gamma-ray Space Telescope in a single week. Usually, in the same time period, the telescope sees five times fewer triggers from all objects across the sky.
These triggers send email alerts to professional astronomers in the field, which led to a unique problem: “Achievement unlocked: Mailbox spammed by a black hole,” David Yu, a scientist at the Max Planck Institute of Extraterrestrial Physics in Germany, who works on the Fermi gamma-ray burst monitor, joked on social media.
The flares are ongoing. Many observatories around the world — including Swift, Fermi, MAXI, INTEGRAL and the Italian Space Agency’s AGILE — will continue to follow the bursts.
Ground-based professional observatories following the activity include the Gran Telescopio Canarias (Spain), the University of Leicester’s 0.5-meter telescope in Oadby (United Kingdom) and Waseda University’s Nasu radio telescope (Japan).
Astronomers may have discovered an exoplanet that has found the elixir to planetary youth, knocking billions of years off its age.
Until now, stellar rejuvenation has been pure conjecture, but after studying a white dwarf star called PG 0010+280, it turns out that one very interesting explanation for an excess in detected infrared radiation may be down to the presence of an exoplanet that was given a facelift.
White dwarf stars are the remnant husks of stars that have died. Eventually, when a star like our sun runs out of fuel, puffing up into a red giant star, its layers of plasma will be blasted into space by powerful, suicidal stellar winds. This will create a beautiful planetary nebula with a small, dense white dwarf in the core. [The Strangest Alien Planets (Gallery)]
But what happens to all this material that has been jetted into space? Well, as the theory goes, some of it may fall onto massive gaseous exoplanets orbiting far away from the star. Before their star ran out of hydrogen and puffed up into a red giant, that exoplanet was aging gracefully, cooling down billions of years after formation.
The situation changed, however, when its atmosphere became bulked up with stellar plasma, re-heating the massive world and making it appear much younger than it really is.
“When planets are young, they still glow with infrared light from their formation,” Michael Jura of the University of California, Los Angeles, co-author of the study published in The Astrophysical Journal, said in a statement. “But as they get older and cooler, you can’t see them anymore. Rejuvenated planets would be visible again
White dwarf studies have gone into overdrive in recent years after astronomers realized they could study white dwarf atmospheres to find the pulverized remains of asteroids and planetary bodies. When passing into the white dwarf phase, the planets and asteroids that are in orbit may drift too close to the powerful tidal forces near that star, and become shredded.
During a survey of white dwarfs for the chemical signatures of these pulverized planetary remains, undergraduate student Blake Pantoja, who was studying at UCLA at the time, came across something weird in data from NASA’s Wide-field Infrared Survey Explorer, and follow-up study by NASA’s Spitzer Space Telescope confirmed the strange excess in infrared light coming from PG 0010+280. At first the team assumed the excess was radiating from a disk of the pulverized remains of asteroids that may have been present — but the data didn’t fit with this explanation.
So two possible explanations remain: perhaps the excess is being generated by a companion brown dwarf (a failed star) or, potentially, a rejuvenated planet, heated up by an influx of stellar matter.
“I find the most exciting part of this research is that this infrared excess could potentially come from a giant planet, though we need more work to prove it,” said Siyi Xu of UCLA and the European Southern Observatory in Germany. “If confirmed, it would directly tell us that some planets can survive the red giant stage of stars and be present around white dwarfs.”
To confirm if this infrared excess is indeed a rejuvenated planet, astronomers are looking to NASA’s James Webb Space Telescope (that is planned for a 2018 launch) for help. Although tantalizing, we’ll have to wait for confirmation as to what this signal is.
The bizarre find is the first of its kind ever discovered by astronomers. The strange, cometlike planet, known as GJ 436b, is orbiting a red dwarf star and is about 22 times as massive as Earth. Astronomers detected the giant gas cloud around the planet using NASA’s Hubble Space Telescope and Chandra X-ray Observatory.
“I was astonished by the mere size of the cloud of gas escaping from the planet,” said study lead author David Ehrenreich, an astronomer at the observatory of the University of Geneva in Switzerland.
GJ 436b, located about 33 light-years from Earth in the constellation Leo, is a kind of world known as a warm Neptune. Such planets, at about 10 to 20 times the mass of Earth, are about the mass of “cold Neptunes” such as Uranus — and, naturally, Neptune — but they are as close, or closer, to their stars than Mercury is to our sun. With an orbit of only about 3 million miles (4.8 million kilometers), “GJ 436b is 33 times closer to its star than Earth is to the sun, and 13 times closer than Mercury,” Ehrenreich told Space.com.
The cloud of gas around GJ 436b, made up mostly of hydrogen, has a circular head that surrounds GJ 436b, and a tail trailing behind the planet. The diameter of the head is about 1.8 million miles (3 million km), or five times the width of the host star, which is about half that of the sun, Ehrenreich said. The length of the tail is uncertain, because the research team’s observations do not cover it entirely, but their computer models suggest it could be about 9.3 million miles (15 million km) long.
Although prior research has predicted that other gas giants should be blowing off cometlike tails, based on how hot they must be due to their proximity to their stars, “GJ 436b is the first planet for which a cometlike tail is confidently detected,” Ehrenreich said. (A previous study revealed indirect evidence of a rocky world that appears to be disintegrating around its host star, creating a cometlike tail of material behind the planet. That study used data from NASA’s Kepler space telescope, which observed scattering of the light from the planet’s host star.)
The scientists estimated that GJ 436b is currently blowing off up to 1,000 tons of gas per second. This means that GJ 436b is currently losing about 0.1 percent of its atmosphere every billion years, which is far too slow a rate to deplete its atmosphere in the lifetime of its parent red dwarf star. However, when the star was more active in its infancy, the researchers estimated that GJ 436b could have lost 10 percent or more of its atmosphere during its first billion years.
Recently, another team of researchers suggested that GJ 436b might possess a helium-rich sky depleted of hydrogen. “However, in order to be really hydrogen-poor and helium-rich, the atmosphere of GJ 436b should have represented a very small fraction of the planet['s] initial mass, around one-thousandth,” Ehrenreich said. “In such a case, the whole atmosphere would have been gone today, which as we measure is not the case.”
Ehrenreich noted that the Kepler spacecraft, as well as NASA’s upcoming TESS space mission and the European Space Agency’s future CHEOPS and PLATO spacecraft “are poised to find thousands of system like GJ 436 in the coming years.” This suggests that many other planets with cometlike tails could soon be discovered.
The scientists now plan to investigate less massive planets, such as “super-Earths” and “mini-Neptunes” to see if they might also have puffy atmospheres and cometlike tails.
“We’re going to study one such object in the course of next year with Hubble, and have proposed to observe several more,” Ehrenreich said.
The scientists detailed their findings online today (June 24) in the journal Nature.
Globular clusters are densely packed collections of ancient stars. Roughly spherical in shape, they contain hundreds of thousands, and sometimes millions, of stars. Studying them helps astronomers estimate the age of a region of space or figure out where the center of a galaxy lies.
There are about 150 known globular clusters in the Milky Way galaxy, according to Georgia State University’s HyperPhysics website. All are estimated to be at least 10 billion years old, and contain some of the oldest stars in the galaxy. The clusters likely formed very early, before the galaxy flattened into a spiral disc.
Some globular clusters, such as Messier 13 (M13) in the constellation Hercules, can be seen with the naked eye. They are pretty to look at, but it was only after telescopes were invented that they began to shine in astronomy circles. With telescopes, it was possible to peer closer at the stars within these clusters. They are mostly low-mass red stars and intermediate-mass yellow stars — none of them greater than 0.8 solar masses, according to HyperPhysics. [Related: How to See the Great Hercules Cluster of Stars]
Some other general observations of globular clusters, according to Pennsylvania State University: they are found in every direction in the sky, the density of stars in a globular cluster is much greater than the density of stars around the sun, and the clusters are not found to contain any gas. The abundance of any elements heavier than helium is only 1 percent to 10 percent of the abundance of the same elements in the sun.
The first two officially discovered and named clusters in the telescopic age were M22 (in Sagittarius, in 1665) and Omega Centauri in Centaurus, according to Encyclopedia Britannica. Like M13, Omega Centauri is also visible to the naked eye, but was not classified as a globular cluster until examined by a telescope.
M22 was a notable find not only for its early discovery, but also for the ages of the stars within it. The stars range between 12 billion and 13 billion years old, which date it close to the formation of the universe 13.8 billion years ago, according to the European Space Agency.
“[Its discovery] is not so surprising as it is one of the brightest globular clusters visible from the Northern Hemisphere, located in the constellation of Sagittarius, close to the Galactic Bulge — the dense mass of stars at the center of the Milky Way,” according to the ESA.
It’s tricky to find M13 with the naked eye, but if the skies are especially dark and clear it is possible, ESA wrote. Omega Centauri and M13 both were discovered by Edmund Halley in the 18th century; Halley is best known as the astronomer who figured out that Halley’s Comet returns to Earth periodically.
“As Halley wrote: ‘This is but a little Patch, but it shews it self to the naked Eye, when the Sky is serene and the Moon absent,’” ESA wrote. Centuries later, M13 was also the target of the Arecibo radio telescope message to extraterrestrials in 1974.
In 1917 astronomer Harlow Shapley, studying Cepheids, a certain kind of variable star within each cluster, noted that these stars shine at a predictable brightness depending on distance from the receiver. He was able to calculate the distances to these stars, which revealed the galactic center is in the constellation Sagitarrius.
Shapley also noted that globular clusters are arranged symmetrically around the galaxy, but that they were arranged equally above and below the galactic plane, seeming to avoid the plane itself.
Shapley’s model greatly increased the size of the galaxy and pushed the solar system — and humanity — farther from the center. However, Shapley believed that the universe was “a single, enormous, all-encompassing unit,” according to the American Institute of Physics. Building on Shapley’s research, Edwin Hubble found globular clusters that were even more distant — as much as 10 times farther — and that lay beyond the Milky Way, in other galaxies. Presented with Hubble’s evidence, Shapley reportedly was glad to see his theories refuted.
The namesake Hubble Space Telescope has been particularly productive when it comes to looking at globular clusters, because they are not obscured by Earth’s atmosphere. With an absence of star twinkling, the stars come into sharper view. This makes it easier to calculate their distance and properties. In one area of the Virgo constellation alone, NASA wrote in a release in 2008, the telescope revealed more than 11,000 globular clusters.
At the same time, the telescope gave hints as to why M87 (which is embedded in the same region) has more star clusters than what would be expected. This is because M87 and clusters like it were created in very dense areas of the universe that provided more favorable conditions for star birth, which takes place in clouds of gas called nebulae.
Hubble also destroyed a long-standing perception among astronomers that globular clusters always contain stars of about the same age. The most massive globular clusters likely grab on to any material that is nearby and birth new generations of stars, NASA wrote in a past release.
What does this mean? Well, it could be that each of the dozens of clusters studied are packed with dark matter or may even by hiding a massive black hole, but neither of the explanations make any sense.
Globular star clusters are ancient ensembles of thousands of stars that can be found orbiting galaxies like our Milky Way. Their study is critical to help us understand how galaxies on the whole evolve as the stars they are known to contain are often as old as the galaxies they orbit.
“Globular clusters and their constituent stars are keys to understanding the formation and evolution of galaxies. For decades, astronomers thought that the stars that made up a given globular cluster all shared the same ages and chemical compositions — but we now know that they are stranger and more complicated creatures,” said Matt Taylor, a PhD student at the Pontificia Universidad Catolica de Chile, Santiago, Chile, and lead author of the study.
Using the FLAMES instrument on the ESO’s Very Large Telescope at the Paranal Observatory in Chile, Taylor and his team surveyed 125 of the around 2,000 globular clusters in orbit around Centaurus A and gauged their masses. Usually, the mass of a globular cluster can be derived by measuring their brightness. The brighter the cluster, the more stars it has and the more massive it is.
Naturally, the researchers’ suspicions are focusing on these clusters amassing a reservoir of dark matter. But globular star clusters are not thought to contain significant quantities of invisible stuff. Perhaps, therefore, these islands of stars have massive black holes in their cores, or maybe a massive graveyard of other stellar corpses, like the burnt-out husks of stars like neutron stars? For now, where this extra baggage comes from remains mystery.
“Our discovery of star clusters with unexpectedly high masses for the amount of stars they contain hints that there might be multiple families of globular clusters, with differing formation histories. Apparently some star clusters look like, walk like, and smell like run-of-the-mill globulars, but there may quite literally be more to them than meets the eye,” added co-author Thomas Puzia, also at the Pontificia Universidad Catolica de Chile.
To widen the search, the researchers are now carrying out a survey of other globular clusters around other galaxies in the hope of finding more of these mysterious “dark clusters.”
“We have stumbled on a new and mysterious class of star cluster! This shows that we still have much to learn about all aspects of globular cluster formation. It’s an important result and we now need to find further examples of dark clusters around other galaxies,” concluded Taylor.
Scientists have spotted a kind of young birthplace for stars in telescope observations for the first time. The newborn star-forming clump in deep space is a giant cloud of gas that may have given birth to dozens of stars a year, researchers say.
The discovery could shed light on galaxy formation in the early universe, when star formation was at its peak, scientists added.
Stars formed at the greatest speed when the universe was between 3 billion and 4 billion years old, a time when galaxies possessed massive star-forming clumps. It was a mystery as to how these clumps arose, since astronomers have not yet seen them form. Now scientists have uncovered a young star-forming clump, one less than 10 million years old, which could help solve that mystery.
“Clumps have been extensively studied so far, but for the first time, we have observed a newly born one,” study lead author Anita Zanella, an astronomer at the French Alternative Energies and Atomic Energy Commission, told Space.com.
Until now, studied clumps usually contained stars more than 100 million years in age, meaning the clumps were correspondingly old, Zanella said. She and her colleagues instead looked for relatively young stars, which in turn could reveal the presence of relatively young clumps.
The astronomers used NASA’s Hubble Space Telescope to discover the clump, which is located in a galaxy nearly 10.4 billion light-years away, dating back to when the universe was only about 3.3 billion years old. The scientists calculated that the clump was about 3,000 light-years wide and more than 1 billion times the mass of the sun.
Based on the light detected from the clump, the researchers estimated that the gas cloud produced “the equivalent of 32 stars with the mass of the sun every year,” Zanella said. This accounted for nearly 40 percent of the stars produced in the galaxy hosting the clump. All in all, “the clump formed stars 10 times more efficiently than normal galaxies,” Zanella said.
By analyzing the initial phase of clump formation, this research favors a theory that suggests star-forming clumps begin as giant, dense pockets in highly turbulent, gas-rich matter in young galaxies. The researchers’ preliminary estimates suggest that giant clumps such as the one they discovered live about 500 million years.
This research suggests that giant clumps are not rapidly destroyed by the energetic winds from the stars they created as some had previously argued. Instead, the clumps could live long enough to migrate toward the centers of galaxies. “Clump migration could thus explain why and how galaxy bulges form,” Zanella said.
Future research with other telescopes could help discover additional young star-forming clumps, yielding insights on galaxy formation, Zanella said. That research could possibly involve the Atacama Large Millimeter Array in northern Chile and the James Webb Space Telescope, whose launch is planned for the end of 2018.
The results, outlined in a new study, show that the disk is about 60 percent larger than previously thought. Not only do the results extend the size of the Milky Way, they also reveal a rippling pattern, which raises intriguing questions about what sent wavelike fluctuations rippling through the disk.
The researchers said the likely culprit was a dwarf galaxy. It might have plunged through the Milky Way’s center long ago, sparking the rippling patterns astronomers have now detected for the first time.
Roughly 15 years ago, Heidi Newberg, an astronomer at the Rensselaer Polytechnic Institute in New York, and her colleagues found a group of stars beyond the disk’s outermost edge. The so-called Monoceros Ring is about 60,000 light-years from the galactic center (just beyond where the disk was thought to end at 50,000 light-years).
Over the years, astronomers were divided into two camps regarding the origins of the ring. Some argued that it was simply a tidal stream: The debris of a dwarf galaxy that fell into the Milky Way and was stretched in the process. Others argued that the ring is a part of the disk. The issue, however, is that the ring is slightly above the plane of the disk. So astronomers in the latter camp attributed that to the fact that the disk flares up toward the edge.
Enter Yan Xu, an astronomer at the National Astronomical Observatories of China. Xu, Newberg and colleagues took a second look at the problem using data from the Sloan Digital Sky Survey. With improved data compared to previous studies, they found four total structures in and just outside what is currently considered the Milky Way’s outer disk. The third structure was the highly debated Monoceros ring, and the fourth structure was the Triangulum Andromeda Stream, located 70,000 light-years from the galactic center.
All four structures alternated with respect to the disk. They went from above it, to below it, to above it, to below it. Newberg, who was in the tidal stream camp, was surprised that the ring and three other structures were actually a part of an oscillating disk.
“We didn’t know how a disk could go up and down,” said Newberg. Luckily, computer simulations by various teams showed that a dwarf galaxy falling into the Milky Way might create a similar pattern. “When it goes through, it can disturb the disk just like a pebble disturbs water in a puddle,” said Newberg. “And that wave can propagate through the disk from that event.”
This new picture makes sense, said Newberg. It even matches observations of the gases in the disk, which have long been observed as rippled. But the implications extend far beyond a corrugated disk.
“If it’s true that the Monoceros Ring and the Triangulum Andromeda structure are part of this oscillatory pattern, then the stellar disk goes out way further than the textbook tells us it ought to be,” said Newberg. Instead of extending nearly 100,000 light-years from one side to the other, it would be more like 160,000 light-years wide.
This brings the Milky Way’s size up to that of Andromeda. The Milky Way’s small radius in comparison to Andromeda’s larger radius has always puzzled astronomers, because the two galaxies have roughly the same mass.
The team plans to further map the rippled disk of Earth’s galaxy and better match their results to models.
The study was detailed in the March 10 edition of the Astrophysical Journal.
The remains of thousands of stars might exist in a vast graveyard near the giant black hole at the heart of our Milky Way galaxy, a region where dead stars feed on companions like zombies and unleash X-ray “howls,” researchers say.
Scientists have long thought that a monster black hole with the mass of 4.3 million suns, named Sagittarius A* (pronounced Sagittarius A star), lurks at the heart of the Milky Way. Recently, astronomers discovered that a surprising number of young, massive stars exist within a few dozen light-years of this black hole.
“These young, massive stars are puzzling because when we think about how stars form from clouds of gas that gravitationally collapse in on themselves, it’s hard to figure how these clouds could have survived long enough to form stars, given the intense gravitational pull of the supermassive black hole that’s so close to them,” lead study author Kerstin Perez, an astrophysicist now at Columbia University in New York, told Space.com.
To learn more about the mysterious center of the galaxy, scientists have focused on X-rays, whose the wavelengths and energies of can shed light on the kinds of activities take place at the galactic center. Previous research has suggested that relatively weak, “soft” X-rays from the galactic core mostly came from white dwarfs — the dim, fading remnants of stars much like the sun — that are accumulating or accreting matter onto themselves.
Now, using NASA’s NuSTAR X-ray space telescope, astronomers have the best pictures yet of the sources of stronger, “hard” X-rays from the area 100 or so light-years away from the Milky Way’s central black hole. However, the nature of these X-ray sources remains a mystery. In a statement, NASA described the signals as possible “screams” from zombie stars.
“As of right now, we haven’t solved any mysteries about the galactic center — we just launched a new, big mystery,” Perez said, who conducted this research while at Columbia University in New York.
Mystery in the Milky Way
The researchers currently have four possible explanations for these hard X-rays; three of those theories involve different kinds of stellar remnants. However, each of these options presents difficulties, Perez said.
One possible explanation points to what is known as an intermediate polar, which is a binary system made up of a white dwarf with a powerful magnetic field that is accreting matter onto itself from a companion star. Intermediate polars are cataclysmic variables, meaning they can brighten in sharp outbursts. [Latest Black Hole Images from NuSTAR Telescope]
If these powerful X-ray sources are intermediate polars, their presence would be puzzling. For example, if intermediate polars are the source of all this radiation, the researchers estimate that 1,000 to 10,000 intermediate polars might exist in the galactic center — about 1,000 times more than observers might have expected.
In addition, the energy of these X-rays suggests that each of the white dwarfs in these intermediate polars has a mass almost as heavy as the sun’s. That is substantially heavier than any intermediate polars that have previously been seen in the galactic center, which have masses that are about half that of the sun’s. “If these are intermediate polars, why are they so heavy?” Perez said. “Did they form from denser clouds of gas, or did they accrete more matter?
Alternatively, these hard X-ray sources might be millisecond pulsars, which are highly magnetic neutron stars that spin about 1,000 times per second. A neutron star is a dense, city-sized stellar remnant born from the explosive death of a larger star. However, when astronomers look at the galactic center in other wavelengths of light besides X-rays, “we don’t see as many millisecond pulsars as we would need to explain these hard X-rays,” Perez said. “Still, prior research has suggested there may be millisecond pulsars hiding in the galactic center.”
In a third theory, these hard X-rays might come from low-mass X-ray binaries. In this scenario, one of the pair of binary stars is either a black hole or a neutron star, while its companion is either a regular star like the sun, an old star such as a red giant or a stellar remnant such as a white dwarf.
However, “low-mass X-ray binaries are inherently unstable, mostly lasting on time scales of 10 years or so,” Perez said. “Maybe there’s something wacky about the environment of the galactic center that makes them more stable.”
One more scenario
The last possibility is that these powerful X-rays do not come from stellar remnants at all, but rather are the results of outbursts of high-energy particles known as cosmic rays, which are coming from the Milky Way’s supermassive black hole and slamming into dense clouds of gas and dust.
“Prior research has postulated that large flares happening on the order of 100 years could travel from the Milky Way’s supermassive black hole and travel through clouds, lighting them up in X-rays,” Perez said. “The difficulty with that idea is that the X-rays don’t match where material is known to be around the galactic center and models that exist right now of how cosmic rays propagate.”
To help solve the mystery behind these powerful X-rays, Perez and her colleagues hope to use NuSTAR to look at the galactic center within the coming year. “Maybe we’ll be able to narrow down these four possibilities,” Perez said.
The eruption was first recognized in 2014, when astronomer Emily Safron, who had just graduated from the University of Toledo in Ohio with her bachelor’s degree, noticed an object in her data that was brightening dramatically over time.
The finding not only marks the earliest eruption ever recorded but also sheds light on how stars grow to be so massive so quickly, researchers reported in a new study.
Stars are born within the clouds of dust and gas scattered throughout most galaxies. Turbulence within the clouds gives rise to knots that begin to collapse under their own weight. The knot quickly becomes a protostar, and continues to grow denser and hotter. Eventually, the central protostar becomes surrounded by a dusty disk roughly equal to it in mass. Astronomers call this a “Class 0″ protostar.
Although a Class 0 protostar has yet to generate energy by fusing hydrogen into helium deep in its core, it still shines, albeit faintly. As the protostar collapses further and accumulates more material from the disk of gas and dust surrounding it, it releases energy in the form of visible light. But this light is often blocked by the surrounding gas and dust.
Studies have shown, however, that the light heats up the dust around the protostar, causing it to give off a faint glow that can then be detected by infrared observatories, like the Spitzer Space Telescope. In this way, astronomers can detect a protostar’s presence via the faint glow of its surrounding dust clouds.
But in 2006, a Class 0 protostar in the constellation Orion, dubbed HOPS 383, acted out of the norm and brightened dramatically. Over two years, it became 35 times brighter. In addition, the most recent data available, from 2012, show that the eruption isn’t fading.
“HOPS 383 is the first outburst we’ve ever seen from a Class 0 object, and it appears to be the youngest protostellar eruption ever recorded,” William Fischer, a postdoctoral researcher at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, said in a statement from NASA.
The new study of HOPS 383 was completed using data from the Spitzer telescope in conjunction with the European Space Agency’s Herschel Space Observatory, as part of a project called the Herschel Orion Protostar Survey (HOPS).
Scientists were also surprised by the length of the eruption, thus making HOPS 383 even more intriguing.
“An outburst lasting this long rules out many possibilities, and we think HOPS 383 is best explained by a sudden increase in the amount of gas the protostar is accreting from the disk around it,” Fischer said.
It’s likely that instabilities in the disk lead to episodes in which large quantities of material flow onto the protostar, Fischer said. This causes the star to develop a hotspot on its surface, which, in turn, heats up the disk and brightens it dramatically.
Such episodes have been observed in older protostars and have been theorized to occur in younger protostars. These episodes could help explain why protostars are dimmer than scientists think they should be, according to the study.
To build up the bulk of a typical star over a short time period, protostars should be brighter, as they should accumulate more material from the surrounding disk faster. Because these protostars are so faint, some astronomers suspect that they could also build up the bulk of a typical star by randomly munching on a lot of material from the surrounding disk, as noted in the study. If that were the case, then astronomers should regularly observe these flashes.
The team will continue to monitor HOPS 383 and has submitted a proposal to use NASA’s Stratospheric Observatory for Infrared Astronomy (SOFIA), the world’s largest flying telescope.
The study was published in the Feb. 10 edition of the Astrophysical Journal.
Supermassive black holes loom in the centers of the majority of massive galaxies. Some of these black holes, like the one in the Milky Way’s center, lie dormant. Others (so-called quasars) actively chow down on gas, causing them to radiate like brilliant beacons of light. They can therefore be seen from across the universe.
Although these monsters clearly accrete huge amounts of matter, some material escapes. It’s flung out into space at close to the speed of light in a jet of plasma. Astronomers don’t understand the physical mechanism at play here, but think it has to do with a strong magnetic field close to the black hole itself.
Luckily, magnetic field lines leave an imprint on any light that passes through them. The magnetic field will twist light so that it is circularly polarized, meaning the electric and magnetic fields rotate continuously as the wave moves, in a corkscrew motion. The stronger the magnetic field, the stronger this imprint.
Until now, only weak magnetic fields located several light-years from the black hole have been caught on camera via this twisting of light. But by looking at higher energies, like the ones visible with ALMA, astronomers can probe more powerful magnetic fields, which lie closer to their black hole counterparts.
“These results, and future studies, will help us understand what is really going on in the immediate vicinity of supermassive black holes,” Muller said in the statement.
Despite the harsh environment created by the monster black hole lurking in the center of the Milky Way galaxy, new observations show that stars — and, potentially, planets — are forming just two light-years away from the colossal giant.
Bright and massive stars were spotted circling the 4-million-solar-mass behemoth more than a decade ago, sparking a debate within the astronomy community. Did they migrate inward after they formed? Or did they somehow manage to form in their original positions?
Most astronomers had said the latter idea seemed far-fetched, given that the black hole wreaks havoc on its surroundings, often stretching any nearby gas into taffylike streamers before it has a chance to collapse into stars. But the new study details observations of low-mass stars forming within reach of the galactic center. The findings lend support to the argument that “adult” stars observed in this region formed near the black hole.
The new evidence for ongoing star formation near the black hole is “a nail in the coffin” for the theory that the stars form in situ, said lead author Farhad Yusef-Zadeh, of Northwestern University. The observations, if accurate, make it unlikely that the stars migrated from elsewhere, the researchers said.
Birth near a black hole
Stars are born within clouds of dust and gas. Turbulence within these clouds give rise to knots that begin to collapse under their own weight. The knots grows hotter and denser, rapidly becoming protostars, which are so-named because they have yet to start fusing hydrogen into helium.
But a protostar can rarely be seen. It has yet to generate energy via nuclear fusion, and any faint light it does produce is often blocked by the disk of gas and dust still surrounding it.
So, when Yusef-Zadeh and his colleagues used the Very Large Array in New Mexico to scan the skies near the central supermassive black hole, they didn’t spot the protostars but rather the disks of gas and dust surrounding them.
“You could see these beautiful cometary-shaped structures,” Yusef-Zadeh told Space.com. Intense starlight and stellar winds from previously discovered high-mass stars had shaped these disks into cometlike structures with bright heads and tails. Similar structures (called bow shocks) can be seen anywhere young stars are being born, including the famous Orion Nebula.
There is, of course, one big catch here — and that is that the tidal force on the black hole is so strong that it’s hard to see how these stars would form,” Yusef-Zadeh said. “Many people think that star formation is forbidden near a supermassive black hole. But nature finds a way.”
Astronomers have managed to find a way as well. Over the last decade, they’ve come up with two scenarios, both of which use the nearby black hole to simulate star formation.
In the first scenario, a cloud might break apart in the strong gravitational field and reassemble into a disk that surrounds the black hole. This disk would then form stars in the same way that the disks surrounding young stars form planets. Although this scenario was first proposed in 2005 by Sergei Nayakshin, an astronomer at the University of Leicester in the United Kingdom, it predicts the formation of low-mass stars. Until now, such stars hadn’t been discovered in the galactic center.
In the second scenario, a cloud gets stretched into a taffylike streamer. But as this happens, the gravitational tide from the nearby black hole does two different things. “It disrupts in one direction, but it squeezes in another direction,” Yusef-Zadeh said. It’s this squeezing, or compressing, that would trigger star formation within the long streamer, Yusef-Zadeh added.
Both scenarios explain why stars encircling the monster black hole, called Sagittarius A*, are found in two rings, or disks, as opposed to random placements.
But some astronomers remain cautious.
“The center of our galaxy is a unique and extreme environment very different from our local solar neighborhood and the rest of the Milky Way,” said Jessica Lu, an astronomer at the University of Hawaii’s Institute for Astronomy. It’s therefore crucial that astronomers don’t jump to any conclusions.
“While these bow shocks have similar shapes to protostars seen in the nearby Orion cluster, there are other ways to produce these bow shocks around small clumps of gas,” Lu told Space.com in an email. [The Strangest Black Holes in the Universe]
Some scientists who do think that stars — even low-mass stars — are forming within a few light-years of supermassive black holes are now starting to wonder if planets are forming there, too.
Typically, a disk circling a protostar will break up into clumps of gas and dust that later become full-fledged planets. But in such an extreme environment, the wind from nearby stars (the same winds that are responsible for the cometlike shapes of the disks seen by Yusef-Zadeh and his colleagues), may also steal mass from these disks. Yusef-Zadeh and his colleagues estimate that there could be enough material left in those disks to form planets.
The team plans to use the Atacama Large Millimeter/submillimeter Array (ALMA) in northern Chile to better probe the disks where the planets may form. ALMA’s high sensitivity will reveal the disks’ masses and maybe even any gaps in the disks, which likely result from forming planets.
“We’re just beginning to really learn about this environment,” Yusef-Zadeh said, adding that he’s excited to start picking away at all of the questions the new study has opened.