Dark matter is five times more plentiful in the universe than regular matter, but it does not emit, reflect or absorb light, making it not just dark but entirely transparent. But if dark-matter particles around black holes can produce gamma-rays (high-energy light), such emissions would give scientists a new way to study this mysterious material.
The process responsible for creating the gamma-rays is somewhat counterintuitive, because it seems to defy two common assumptions: that nothing can escape from a black hole and that there’s no such thing as a free lunch.
Jeremy Schnittman is a theoretical astrophysicist at the NASA Goddard Space Flight Center, and he’s beginning a project to look through data from the Fermi Gamma-ray Space telescope for signs of high-energy light around the edge of a black hole that might have been created by dark matter.
“We’re really just getting started on this part of the problem,” Schnittman said. “As a theoretical astrophysicist, I haven’t done a lot of data analysis in my career, so it’s a little bit of a learning curve for me. But fortunately I’m surrounded by people here at Goddard who are real experts at the Fermi data.”
Schnittman’s search for this dark-matter signal began with a computer program that he has been developing for about 10 years. It models in 3D the paths of particles as they zip through space near a black hole, while some of them get close enough to orbit around the black hole or fall in.
Just over a year ago, he decided to adjust the program to model dark-matter particles. The resulting video shows how the subatomic bits get caught up in the gravitational pull of the black hole and swirl around it in a region called the ergosphere (where all particles must orbit in the direction of the black hole’s spin). Some of the particles collide and destroy each other (also known as annihilation), and this produces a pair of gamma-rays.
These particles of light might normally fall into the black hole, helpless against its gravitational pull, were it not for something called the Penrose process.
In 1971, astrophysicist Roger Penrose showed that if two photons are created very close to a black hole, it’s possible for one of them to escape, while the other falls in. This flies counter to the commonly held idea that nothing can escape from a black hole, or at least nothing that goes past the “event horizon” — the point at which the gravitational pull is so strong that nothing, not even light, can ever exert enough force to get away.
According to the Penrose principle, the particles are not created beyond this point of no return, but under normal circumstances, it’s unlikely that either particle would have any means of getting away from the black hole. So the Penrose process still changes the fate of at least one particle, giving it an escape route.
In 2009, a group of researchers showed that the Penrose process could be applied to dark-matter particles that annihilate and form two gamma-rays. If dark-matter particles are annihilating near the surface of a black hole, telescopes on Earth could detect the escaping gamma-rays.
Schnittman’s work using the 3D computer model has shown many more paths that the particles can take, including some that are more likely to produce gamma-rays that can escape the black hole, and with even higher energies than had been previously predicted. A brief description of those results was published in the journal Physical Review Letters last December, and a longer description of the work has been accepted to the Astrophysical Journal.
With those results, Schnittman and his colleagues are now looking for this signal, although they said they expect it to be very dim compared to many other gamma-ray sources. The researchers are creating a list of target galaxies that have few gamma-ray sources and very massive black holes.
“The bigger the black hole, the bigger the signal,” Schnittman said. “It scales in a way that as your black hole [mass] goes up by a factor of 10, the expected signal goes way up, by something like a factor of 1,000.
“The first pass at observing this effect is almost certainly not going to yield an actual detection. But it will provide probably the strongest upper limit on this type of process that has ever been seen before — the idea of high-energy dark-matter particle reactions. Even that is progress.”
The particles that escape the black hole via the Penrose process not only go free, but they also leave with more energy than they started with. In fact, they have more energy than the pair of particles had combined. This, it would seem, is a free lunch.
Since Penrose’s original work, scientists have shown that not only does the escaping particle steal energy from its partner (essentially pushing off the other particle), but it also steals energy from the spinning black hole. Every Penrose particle that escapes slows the spin of the black hole by a very, very tiny amount.
(When he originally proposed the idea, Penrose wrote that this phenomenon could be used by an advanced society as an energy-producing garbage disposal, in which the garbage serves as the particle that falls into the black hole, producing a flux of high energy particles that escapes.)
Schnittman said he is reserved in his hopes for finding a dark-matter signal in the Fermi data. Not only will it be difficult to see such a small signal amid the noise of gamma-rays in the universe, but the existence of the signal also relies on a major unknown: whether or not dark-matter particles create gamma-rays when they annihilate.
The fact is, scientists don’t know what dark matter is made of, and they don’t know if dark-matter particles will annihilate in the way that Schnittman’s model predicts, if they do so at all. So if Schnittman did find a signal, it would mean a major breakthrough in the study of the nature of dark matter.
“That’s Nobel Prize kind of stuff,” Schnittman said. “It’s a long shot, but it would be a tremendous payoff if we found actual confirmation of dark-matter annihilation.”
Saturn’s icy moon Enceladus is looking better and better as a potential abode for alien life.
Chemical reactions that free up energy that could potentially support a biosphere have occurred — and perhaps still are occurring — deep within Enceladus’ salty subsurface ocean, a new study suggests.
This determination comes less than two months after a different research team announced that active hydrothermal vents likely exist on Enceladus’ seafloor, suggesting that conditions there could be similar to those that gave rise to some of the first lifeforms on Earth.
Astrobiologists regard the 314-mile-wide (505 kilometers) Enceladus as one of the solar system’s best bets to host life beyond Earth.
The satellite is covered by an icy shell, but it’s geologically quite active, as evidenced by the powerful geysers that blast continuously from its south polar region. These plumes contain significant amounts of water, which scientists think originates from a subsurface ocean.
Previous studies have suggested that this ocean is in contact with Enceladus’ rocky mantle, making possible all sorts of interesting chemical reactions. The new paper, published Wednesday (May 6) in the journal Geochimica et Cosmochimica Acta, further supports that notion.
The researchers studied mass-spectrometry measurements of the gases and ice grains in Enceladus’ plumes made by NASA’s Cassini spacecraft, which has been orbiting Saturn since 2004. The team used this information to develop a model that estimates the saltiness and pH of Enceladus’ plumes, and, by extension, the moon’s underground ocean.
The scientists determined that the ocean is likely salty and quite basic, with a pH of 11 or 12 — roughly equivalent to that of ammonia-based glass-cleaning solutions, but still within the tolerance range of some organisms on Earth. (The pH scale runs from 0 to 14. Seven is neutral; anything higher is basic, and anything lower is acidic.)
Enceladus’ subsurface sea contains dissolved sodium chloride (NaCl) — run-of-the-mill table salt — just as Earth’s oceans do, researchers said. But it’s full of sodium carbonate (Na2CO3), which is also known as washing soda or soda ash, as well.
So this alien water body is probably more similar to terrestrial “soda lakes,” such as Mono Lake in California, than it is to the Atlantic and Pacific oceans, study team members said.
Such inferences shouldn’t dishearten astrobiologists; a variety of lifeforms thrive in Mono Lake, including brine shrimp and many different types of microbe. And the new study provides other reasons to be optimistic about Enceladus’ life-hosting potential, researchers said.
For example, the team’s model suggests that the subsurface ocean’s high pH is generated by a process called serpentization, in which certain kinds of metallic rocks from Enceladus’ upper mantle are transformed into new minerals (including serpentine, hence the name) via interactions with water.
In addition to raising pH, serpentization results in the production of molecular hydrogen (H2) — a potential source of chemical energy for any lifeforms that may exist in the underground sea, researchers said.
”Molecular hydrogen can both drive the formation of organic compounds like amino acids that may lead to the origin of life, and serve as food for microbial life such as methane-producing organisms,” study lead author Christopher Glein, of the Carnegie Institution for Science in Washington, said in a statement.
“As such, serpentinization provides a link between geological processes and biological processes,” he added. “The discovery of serpentinization makes Enceladus an even more promising candidate for a separate genesis of life.”
Sunlight probably doesn’t flow through Enceladus’ underground sea, but any microbes that exist there may thus have access to two different sources metabolism-supporting energy sources — molecular hydrogen and the heat provided by hydrothermal vents.
More than 40,000 citizen stargazers have helped to classify over 2 million celestial objects and identify five never-before-seen supernovas, in a massive example of citizen science at work.
An amateur astronomy project of cosmic proportions, established by scientists at the Australian National University, asked volunteers to look through images taken by the SkyMapper telescope and search for new objects, with a particular focus on finding new supernovas.
The project was set up using the Zooniverse platform (run by the University of Oxford), which hosts many other citizen science projects, and which was promoted on the BBC2 TV series “Stargazing Live,” from March 18 to March 20. [Supernova Photos: Great Images of Star Explosions]
To participate in the project, volunteers signed up online and accessed the Zooniverse platform, which walked them through their tasks.
Zooniverse has hosted many space-related citizen science projects in the past, including hunts for alien planets, “space warp” galaxies and holes in cosmic clouds.
The participants were asked to look at star-filled patches of the night sky, taken by the SkyMapper telescope. The volunteers would look at images of the same region taken at different times, and search for changes that could indicate the presence of different celestial objects.
A supernova, for example, is a large star that has burned up most of its fuel and dies in a great explosion. A supernova eruption can briefly outshine all the light created by all the stars in an entire galaxy — so even a star that is normally too distant to see with a telescope may suddenly become visible if it explodes into a supernova. This means a SkyMapper volunteer might see a point of light appear where there previously was none.
“One volunteer was so determined to find a supernova that he stayed online for 25 hours. Unfortunately, he didn’t find one, but he did find an unusual variable star, which we think might explode in the next 700 million years or so,” Richard Scalzo, a researcher working with the SkyMapper telescope at the Australian National University (ANU) Research School of Astronomy and Astrophysics, said in a statement from ANU (a variable star is one that changes in brightness when observed from either, either due to changes in the star itself or something between the star and the observer). “It was a huge success. Everyone was really excited to take part.”
That excitement paid off, as the project required multiple volunteers. If one of the citizen scientists spotted a possible supernova or some other change in the sky images, then additional volunteers would examine that same region.
If the citizen observers confirmed a new object, then the professional scientists would do a more extensive background check in that region of the sky, Scalzo said in an email. After that, the scientists looked at the object’s spectra, a breakdown of the light the object emits. This can tell scientists all kinds of information about the object’s makeup and its history.
“Once we have at least one spectrum, we consider what other science we could do,” Scalzo said. “Type Ia supernovae can be used to study the expansion history of the universe and dark energy. Other kinds of supernovae can be used, singly or in large groups, to learn more about how different kinds of stars end their lives.”
Scalzo said the project required the assistance of so many human helpers because the computer programs need assistance. “Computers are very good at identifying supernova,” he said, “but you need a lot of data to train them.”
In other words, the scientists have to provide the computer program with lots of examples of what the supernova look like; it isn’t as simple as telling the computer to look for changes in the sky images.
“A few years ago, before SkyMapper was ready to take data, another group called the Palomar Transient Factory (PTF) partnered with the Zooniverse to allow volunteers to hunt for supernovae,” Scalzo said. “Over a few years, PTF found more than 500 real supernovae with the help of Zooniverse volunteers, and used the data to train a machine-learning algorithm to recognize supernovae more accurately than the volunteers could.”
The SkyMapper telescope has only identified 15 supernova, so Scalzo said there is still work to do to improve the programs.
The five newly discovered supernovas have already made their way into a cosmological study of dark energy by the SkyMapper scientists, but Scalzo said there is more work to be done before the results of that study are published. He added that there may be more work for citizen scientists to do with SkyMapper data in the future.
In the search for life beyond Earth, the mantra has usually been, “Follow the water.” But now, scientists say it may be possible for a waterless environment to give rise to alien life.
In a recent study, researchers at Cornell University proposed a formula for life that could thrive on Saturn’s largest moon, Titan. With its freezing temperatures, seas of liquid methane and toxic atmosphere devoid of any liquid water, it may seem unlikely that Titan could give rise to life. But in such environments, it may be possible for there to be methane-based, oxygen-free extraterrestrial life, the researchers said.
On Titan, temperatures of minus 292 degrees Fahrenheit (minus 180 degrees Celsius) would make it difficult for processes like metabolism and reproduction to occur. But the theorized cell membrane, which houses the cell’s organic matter, is composed of nitrogen instead of water, allowing it to do just that. [5 Bold Claims of Alien Life]
On Earth, living cells have a strong, permeable, water-based barrier called a lipid bilayer membrane. But that concept works only in environments with liquid water, so when astronomers are searching for life outside our solar system, they zoom in on small rocky exoplanets orbiting inside a star’s habitable zone — the band where liquid water can exist. But plenty of exoplanets (and even solar system moons) exist well outside this range, where liquid water can’t exist.
So astronomers have long been fascinated by nonaqueous life, and even the possibility that Titan may host methane-based life. Other than Earth, it is the only place in our solar system with liquid seas on its surface. It also hosts a mysterious process that consumes hydrogen, acetylene and ethane, the researchers said. All of these elements flow down from the atmosphere but never quite make it to the surface. So, could life be gobbling them up?
To investigate this possibility, Jonathan Lunine, an astronomer at Cornell University, collaborated with James Stevenson, a graduate student, and his adviser, Paulette Clancy, both of whom work at Cornell’s Chemical and Biomolecular Engineering Department.
“We’re not biologists, and we’re not astronomers — but we had the right tools,” Clancy said in a statement. “Perhaps it helped, because we didn’t come in with any preconceptions about what should be in a membrane and what shouldn’t. We just worked with the compounds that we knew were there and asked, ‘If this was your palette, what can you make out of that?’”
The researchers were able to model a cell that supports metabolism and reproduction but that’s constructed from nitrogen, carbon and hydrogen-based molecules — all of which are known to exist within Titan’s frigid seas. Like a lipid bilayer membrane here on Earth, it’s both rigid and flexible, controlling the transportation of materials in and out of the cell.
They named their theorized cell membrane an “azotosome.” (Azote is French for nitrogen, and lipsome is Greek for “lipid body,” so “azotosome” means “nitrogen body.”)
So far, the researchers have only shown that azotosomes could exist based on molecular simulations.
“Ours is the first concrete blueprint of life not as we know it,” Stevenson said. The next step will be to demonstrate in the laboratory how such membranes function in a methane environment. In the long run, scientists might also be able to model possible observable indicators of alien life.
If life does exist on Titan, it would demonstrate that methane, in addition to water, could be an indicator of life, and that life could more easily populate the cosmos.
Earlier this month, researchers made two big announcements: Saturn’s moon Enceladus likely harbors hot springs, and Jupiter’s huge satellite Ganymede apparently possesses a subsurface ocean that may contain more water than all of Earth does.
However, while the discovery makes Enceladus, which also has a subsurface ocean, even more intriguing to astrobiologists, Ganymede is still not a great bet for alien life, researchers say. [6 Most Likely Places for Alien Life in the Solar System]
Enceladus is the sixth-largest of Saturn’s moons, with a diameter of only about 314 miles (505 kilometers). Despite its tiny size, Enceladus has drawn a great deal of attention due to its erupting water geysers, first seen by NASA’s Cassini spacecraft in 2005. Now, scientists have found that Enceladus may have hot springs under its frozen crust. The discovery that the floor of its hidden ocean may be home to near-boiling temperatures is the first evidence of active hydrothermal vents beyond the oceans of Earth.
“This surely has implications regarding astrobiology, life-searching and all those kinds of topics,” said study author Hsiang-Wen Sean Hsu, a planetary scientist at the University of Colorado, Boulder.
Specifically, these new findings suggest that the conditions on Enceladus’ seafloor are similar to those found on Earth in a deep-sea field of hydrothermal vents known as Lost City in the Atlantic Ocean, which is home to a wide variety of animals, such as eels, snails, mussels, worms, shrimplike amphipods and flealike ostracods, said Gabriel Tobie, a planetologist at the University of Nantes in France.
Lost City consists of 196-foot-tall (60 meters) limestone chimneys that release alkaline fluid that is low in metals and lower than boiling temperature. In contrast, most other known hydrothermal vents on Earth give off metal-rich acidic fluid that is hotter than boiling temperature.
Alkaline hydrothermal vents might have been the birthplace of the first living organisms on the early Earth, supplying key nutrients and energy, Tobie said.
“For Enceladus, the new discovery of hot vents enhances its chance for life,” Tobie told Space.com.
NASA also announced that a salty ocean hides beneath the icy crust of Ganymede, the largest moon in the solar system. Scientists using NASA’s Hubble Space Telescope found that Ganymede’s ocean could harbor more water than is found on Earth. Ganymede’s sea may be about 60 miles (100 km) deep — 10 times the depth of Earth’s oceans.
However, this finding does not necessarily raise Ganymede’s chances for life, Tobie said.
“A major difference between Enceladus and Ganymede is the difference of pressure at the base of the ocean,” Tobie said. The pressure at the base of Enceladus’ ocean is rather low, at 50 to 100 bar — or about 50 to 100 times the atmospheric pressure of Earth at sea level. This low pressure permits water from circulating in underlying porous rocks, thus helping to drive chemical reactions that could lead life to emerge.
In contrast, the pressure at the base of Ganymede’s ocean is much higher — about 15,000 to 20,000 bar, Tobie said. Under such high pressure, not only is rock less porous, but water can form a kind of ice.
“A very thick layer of high-pressure ice more than 400 kilometers [250 miles] thick will form at the base of the ocean,” Tobie said. “Even if deep hot vents exist on Ganymede, the chance for life seems rather low due to the formation of this high-pressure ice layer.”
However, Ganymede is not the only watery moon of Jupiter. Prior research suggests that Europa, the fourth-largest moon of Jupiter, may possess both an ocean beneath its icy surface and hot springs.
“Like in Enceladus, the ocean in Europa would be directly in contact with the rock core, which will favor water-rock interactions and exchange of nutrients with the ocean,” Tobie said.
“Both Europa and Enceladus have a high astrobiological potential,” he added. “But for the moment, it is only a potential. Only future missions with in situ investigations will really answer if it is more than only a potential.”
Cosmic detectives are investigating a case of mistaken stellar identity: An exploding star that was once thought to be the oldest recorded nova — a nuclear explosion on the surface of a dead star — was more likely caused by the merger of two stars.
In 1670, a bright new star appeared in the constellation Cygnus, the Swan, and stayed there for two years — you can see the location of the new stars in this video. The short-lived star was grouped into the “nova” category, but over the last 30 years, astronomers have been questioning its identity.
A new research paper that examines the chemical makeup of the crime scene may be the final nail in the coffin. The researchers suggest that the so-called nova is instead the oldest example of another type of stellar explosion sometimes called a “red nova” — a somewhat newly-discovered phenomenon that scientists are still working to understand.
In 1670, a new star appeared just above the head of the swan that makes up the constellation Cygnus. Many astronomers took note of this newcomer, so its appearance and life span are well documented. It was dubbed Nova Vul 1670 —at the time, “nova” referred simply to any new star.
In the last 300 years, however, the word “nova” has taken on a much more specific and scientific meaning.
By today’s definition, a classic nova is an explosion that takes place on the surface of a white dwarf — the small, dense, nugget of leftover material from a star that has stopped burning. The white dwarf syphons material away from another nearby star, the pressure builds up on its surface and a nuclear reaction releases an incredible burst of energy. (Unlike Type Ia supernovas, which start in a similar fashion, the white dwarf in a nova is expected to survive through the explosion.)
Many things about CK Vulpeculae’s identity as a nova just don’t line up, said Tomasz Kaminski, a postdoctoral fellow at the European Southern Observatory.
For example, novas tend to burn in the sky for days — not years, as CK Vulpeculae did. Plus, the new star of 1670 didn’t disappear right away. After two years, it faded, then reappeared, then faded for good — which is very unusual for a nova, Kaminski said. And observations have shown that CK Vulpeculae’s temperature is much lower than that of a nova, where the radiation from the nuclear reaction continues to generate heat after the explosion is done, Kaminski said.
The new study, which is detailed in the March 23 edition of the journal Nature, may finally strip CK Vulpeculae of its “nova” title. Kaminski and his co-authors looked at the different molecules present in the wreckage of CK Vulpeculae, and found a profile that they say cannot be created by a classical nova.
But if isn’t a nova, then what is it?
In the new paper, Kaminski and his colleagues argue that CK Vulpeculae is a phenomenon with multiple names in scientific literature. They’ve been called red novas, red transients, luminous red transients and intermediate luminous optical transients (ILOTs), among others.
“People who study these red nova realized all the observations we have of these objects can be explained only if they explode as [an] effect of a collision and a merger of two stars,” Kaminski said.
The notion that a red nova could be a unique category of stellar explosion took hold in 2008, when astronomers watched two stars in a system orbit in toward each other and produce an explosion with the characteristics of a red nova, Kaminski said.
“Many of the novae we know from historical records could be this type; it’s just that people observe them during the outburst, and then no one really cared what happened with them,” Kaminski said. “And that’s why they didn’t realize maybe we’re dealing with some new phenomenon.”
Previous groups have suggested that CK Vulpeculae is a red nova. What Kaminski and his group have provided is the first look at the molecular profile of one of these objects, which he said is distinct from other stellar explosions. [Star Quiz: Test Your Stellar Smarts]
“This is a major step,” he said. The chemical profile shows the presence of molecules and isotopes that are strange compared to other types of stellar explosions, including classical novas, Kaminski said. In fact, the profile is actually somewhat unique among red nova, which may be a product of CK Vulpeculae’s age — perhaps something happens in these red novas over time that produces a unique bouquet of chemicals, he said.
The researchers made their observations with the submillimeter-wavelength Atacama Pathfinder Experiment (APEX) telescope and Effelsberg radio telescope.
Kaminski cautioned that scientists are still working to demonstrate that red novas are, in fact, the products of stellar mergers.
Noam Soker, an astrophysicist at the Technion Israel Institute of Technology, was one of the scientists who previously suggested that CK Vulpeculae was a red nova. He and some of his colleagues have theorized that red novas are not the result of suddenly stellar mergers but rather are produced by the gradual accretion of matter from one star to another. He and Kaminski said one thing that would help clarify the cause of a red nova would be observations inside the clouds of debris, to see the stars that remain there.
Kaminski said that, right now, the available evidence suggests that CK Vulpeculae is a red nova. But it’s possible that in 10 years, someone will come up with a different explanation for how this stellar explosion came to be.
“This is science and astronomy: You propose something new, and everyone is welcome to find supporting evidence, or disprove it with some new theory or new observations,” he said.
This finding, which was made by the SOFIA flying observatory, may shed light on how the dust that helped form countless stars and galaxies was created, the scientists added.
The elements that make up everything from people to planets are essentially stardust. These elements are forged in stars by nuclear fusion, which fuse small atoms such as hydrogen and helium into larger ones such as carbon and iron. [Supernova Photos: Amazing Star Explosions]
For years, scientists have tried to explain the vast amounts of dust seen in the early universe. The leading explanation was that this dust was created by exploding stars known as supernovas.
However, researchers also thought supernovas should excel at shattering and destroying dust as well. Prior research suggested that up to 80 percent or more of the dust that supernovas might generate could get destroyed by the so-called “reverse shocks” of these explosions. Reverse shocks are shockwaves rebounding off the cold, dense matter surrounding supernovas.
“It’s been known that ‘we are all made of star stuff,’ but the details of how newly formed ‘star stuff’ survives to later become the seeds for stars and planets is a bit murky,” said lead study author Ryan Lau, an astronomer at Cornell University.
One potential alternative source of the ancient dust seen in the early universe was that “some less powerful stars that don’t go supernova go through a phase where they gently blow off their innards and form dust,” Lau said. “However, this way of forming dust isn’t very efficient, because it takes a while for these less powerful stars to evolve to that point.”
Now Lau and his colleagues have unexpectedly confirmed that supernovas can be dust factories.
“Finding this surviving dust is surprising to me because when I think of a supernova, I imagine a very harsh, violent environment that is very inhospitable to dust and other things that happen to be caught in the explosion,” Lau told Space.com.
The astronomers employed the Stratospheric Observatory for Infrared Astronomy (SOFIA), a joint project of NASA and the German Aerospace Center housed aboard a modified Boeing 747SP jumbo jet. They analyzed dust in the middle of Sgr A East, the remnant of a supernova located near the center of the Milky Way. This remnant, known as Sgr A East, is about 10,000 years old.
“We were on a flying observatory traveling at 600 mph (965 km/h) at an altitude of 45,000 feet (13,715 meters) to take images of a 10,000-year-old supernova remnant located 27,000 light-years away from us at the center of our galaxy,” Lau said. “No other currently operating observatory other than the Stratospheric Observatory for Infrared Astronomy could detect this dust.”
The scientists found that about 7 to 20 percent of the initial dust of the supernova survived its reverse shock.
“One of the most surprising things is that we were not expecting to see this at all,” Lau said. “We were looking at the two brighter features to the right and to the left of the supernova dust we found.”
The researchers suggest the dust survived the supernova’s reverse shock because of dense gas surrounding the explosion, which slowed the debris from the supernova, helping the dust cool greatly and preventing its destruction. This finding implies that ancient supernovas could have generated the vast amounts of dust seen in the early universe.
The scientists detailed their findings online today (March 19) in the journal Science.
A decade ago, a tiny but mighty probe descended into the soupy atmosphere of Titan. This moon of Saturn is of great interest to astrobiologists because its chemistry and liquid cycle remind us of what the early Earth could have looked like before life arose.
The probe, called Huygens, made it to the surface and transmitted imagery all the way. It remained alive on the surface for more than an hour, transmitting data to NASA’s orbiting Cassini spacecraft for later analysis by scientists.
During long-term missions, sometimes it takes years to examine all the data gathered by probes because there is so much for investigators to parse through. A decade later, we are only now starting to understand how the atmosphere of Titan formed, mostly based on what Huygens observed in January 2005.
The data could help settle a debate about how Titan got its atmosphere, said Christopher Glein, a postdoctoral researcher at the University of Toronto in Canada.
One scenario, more popular before Huygens reached the surface, suggested that the moon nabbed nitrogen, methane and noble gases that were floating in the solar system during formation. Another theory, and one that Glein supports, holds that the atmosphere was generated within Titan as a consequence of hydrothermal activity.
“That’s the idea I am exploring — producing gases inside of Titan,” Glein said.
His new paper, titled “Noble gases, nitrogen, and methane from the deep interior to the atmosphere of Titan,” was published in the journal Icarus.
Seeking noble gases
The Huygens probe found an isotope of argon — a noble gas also found in Earth’s atmosphere — that appeared to be made within Titan’s presumed rocky core. Argon-40 is a radioactive product that is formed from the radioactive decay of potassium-40. It originated inside of Titan, Glein said, and then got into the atmosphere by some means, perhaps by venting, or through cryovolcanism (cold volcanoes that may erupt mixtures of liquid water).
How the gas was released is a reflection of geophysical processes that depend on Titan’s internal structure. Perhaps Titan is even warmer than thought. Some models predict that Titan’s interior should be warm, but for that to happen its structure would need to be differentiated.
This could mean that Titan has (or once had) a hot rocky core surrounded by an ocean with an icy shell overlaid on top. This would be similar in structure to what is hypothesized on Jupiter’s satellite Ganymede, the largest moon in the solar system, and unlike that of Callisto, another large moon of Jupiter that is mostly undifferentiated, Glein said. [Amazing Photos: Titan, Saturn's Largest Moon]
“There’s not unanimous agreement,” he added. “The key observation is the gravity field — which tells us how much mass separation occurred during the formation and evolution of Titan. If there is a rocky core and ocean-ice shell, there should be a great deal of separation. But Titan is a no-man’s land of ambiguity between Ganymede and Callisto. We can’t be definitive yet.”
Glein’s contribution to the body of knowledge on the origin of Titan’s atmosphere was to create a mathematical representation of Titan’s volatile element geochemistry, assuming that the moon is differentiated and the noble gases originated from the rocky core.
“I did some calculations and connected the dots together. This could all make sense in terms of a larger story,” he said
Glein assumed the building blocks of Titan would have a chemistry similar to a certain kind of ice that is reflective of primitive solar system material, such as comets. The carbon dioxide and ammonia found in these small bodies can produce methane and nitrogen if they are cooked in a hydrothermal system. Inside of Titan, it’s possible this combination would account for the nitrogen and methane that now reside in its atmosphere.
According to Glein, some noble gases behave very similarly (in terms of how easily they form gases) to methane and nitrogen, which are the gases that give Titan an atmosphere. For example, nitrogen is similar to argon, and methane behaves similarly to krypton. These noble gas analogies allowed Glein to calculate how much methane and nitrogen can go from the rocky core to the atmosphere, a distance of at least 300 miles (500 kilometers).
For example, standard models show that the whiff of argon-36 detected by Huygens can be explained if only 2 percent of the total amount in the core make it out to the top. Similarly, nitrogen should also bleed outwards at about 2 percent, and Glein found that this is enough to explain the amount of nitrogen we find in Titan’s atmosphere. He came to a similar conclusion using krypton to estimate the outgassing percentage for methane.
The challenge is that much of the work is based on a single mission and only a few hours of data. While Cassini still makes regular flybys past Titan, its instruments (coupled with the greater distance) are not sensitive enough to gather precise abundances of trace noble gases that would improve on the Huygens results. Similarly, telescopic observations are hard because Titan is too far away for this exacting work.
“I think ultimately we are going to need another mission to Titan, such as a rover, and I think probably the Jupiter system more in the immediate future. There is useful information out there,” Glein said.
“One of the next questions is trying to address why Ganymede and Callisto don’t have atmospheres, like Titan,” he added. “If we can get new data from Ganymede especially, we can test this model and get a general understanding of what’s going on. This is also a key next step in testing the hypothesis of a hydrothermal solar system, where heat sources inside icy worlds allow liquid water to persist, and drive geochemical transformations of carbon and nitrogen. This could set the stage for subsurface life.”
NASA’s forthcoming Juno mission arrives at Jupiter in 2016, and could help in terms of measuring Jupiter’s global water abundance and explaining how its moons were formed from the gas cloud that birthed Jupiter, Glein said. Further ahead is Europe’s JUICE mission, which will look at several of Jupiter’s icy moons in the 2030s and could gather more information on Ganymede’s chemistry and interior.
Astronomers have discovered the largest and most luminous black hole ever seen — an ancient monster with a mass about 12 billion times that of the sun — that dates back to when the universe was less than 1 billion years old.
It remains a mystery how black holes could have grown so huge in such a relatively brief time after the dawn of the universe, researchers say.
Supermassive black holes are thought to lurk in the hearts of most, if not all, large galaxies. The largest black holes found so far in the nearby universe have masses more than 10 billion times that of the sun. In comparison, the black hole at the center of the Milky Way is thought to have a mass only 4 million to 5 million times that of the sun.
Although not even light can escape the powerful gravitational pulls of black holes — hence, their name — black holes are often bright. That’s because they’re surrounded by features known as accretion disks, which are made up of gas and dust that heat up and give off light as it swirl into the black holes. Astronomers suspect that quasars, the brightest objects in the universe, contain supermassive black holes that release extraordinarily large amounts of light as they rip apart stars.
So far, astronomers have discovered 40 quasars — each with a black hole about 1 billion times the mass of the sun — dating back to when the universe was less than 1 billion years old. Now, scientists report the discovery of a supermassive black hole 12 billion times the mass of the sun about 12.8 billion light-years from Earth that dates back to when the universe was only about 875 million years old.
This black hole — technically known as SDSS J010013.02+280225.8, or J0100+2802 for short — is not only the most massive quasar ever seen in the early universe but also the most luminous. It is about 429 trillion times brighter than the sun and seven times brighter than the most distant quasar known.
The light from very distant quasars can take billions of years to reach Earth. As such, astronomers can see quasars as they were when the universe was young.
This black hole dates back to a little more than 6 percent of the universe’s current age of 13.8 billion years.
“This is quite surprising because it presents serious challenges to theories of black hole growth in the early universe,” said lead study author Xue-Bing Wu, an astrophysicist at Peking University in Beijing.
Accretion discs limit the speed of modern black holes’ growth. First, as gas and dust in the disks get close to black holes, traffic jams slow down any other material that’s falling into them. Second, as matter collides in these traffic jams, it heats up, emitting radiation that drives gas and dust away from the black holes.
Scientists still do not have a satisfactory theory to explain how these supermassive objects formed in the early universe, Wu said.
“It requires either very special ways to quickly grow the black hole or a huge seed black hole,” Wu told Space.com. For instance, a recent study suggested that because the early universe was much smaller than it is today, gas was often denser, obscuring a substantial amount of the radiation given off by accretion disks and thus helping matter fall into black holes.
The researchers noted that the light from this black hole could help provide clues about the dark corners of the distant cosmos. As the quasar’s light shines toward Earth, it passes through intergalactic gas that colors the light. By deducing how this intergalactic gas influenced the spectrum of light from the quasar, scientists can deduce which elements make up this gas. This knowledge, in turn, can provide insight into the star-formation processes that were at work shortly after the Big Bang that produced these elements.
“This quasar is the most luminous one in the early universe, which, like a lighthouse, will provide us chances to use it as a unique tool to study the cosmic structure of the dark, distant universe,” Wu said.
An explosion on the surface of a dying star has is helping to clear up a mystery behind copious amounts of lithium seen in the universe.
By studying Nova Delphini 2013 (V339 Del), astronomers were able to detect a precursor to lithium, making the first direct detection of the third lightest element whose abundance had long remained in the theoretical realm.
“There have been no direct observational evidence for lithium production in novae before our result,” lead author Akito Tajitsu, of the National Observatory of Japan, told Space.com via email. “But many scientists made predictions about it.”
When V339 Del was spotted by an amateur astronomer on Aug. 14, 2013, it was just beyond the limit of being visible to the naked eye, though it was visible in binoculars and telescopes. Within two days, it had brightened enough to be seen without instruments in regions without too much light pollution, the first naked-eye nova since 2007.
Novae form when material from one star in a close binary surface is dumped onto the surface of its white dwarf companion. The runaway thermonuclear reaction causes the surge in brightness, which in turn creates more complex elements than the hydrogen and helium that dominate the inside of most stars.
One element predicted to form in the outburst is the most abundant isotope of lithium, lithium-7 (Li-7). While most heavy elements form inside of stars and through supernovae, lithium-7 is too fragile to withstand the high temperatures found within most stellar cores.
“Lithium is one of the so-called ‘light elements,’ together with beryllium and boron. These elements are much less abundant in the Milky Way and in the Solar System than their neighbors on the periodic table,” Margarita Hernanz, of the Institute of Space Sciences in Spain, told Space.com by email. Hernanz, who studies the late stages of stellar evolution, including explosions, was not part of the research project.
“They are not formed only inside of stars like the others. Their synthesis relies on processes less efficient than nuclear reactions inside the stars.”
Some of the lithium in the universe formed when the universe first got started, during the Big Bang. Cosmic rays interacting with stars and interstellar matter may have formed more. But these events do not provide enough lithium to equal the amount of the element present today.
In the 1950s, scientists suggested that an isotope of beryllium (Be-7) could form near the surface of the star. If the fresh Be-7 was transported to the cooler outer regions before it decayed into Li-7, the temperatures would not destroy the new element. But the difficulty in observing lithium from the ground made it a challenge to verify observationally — until now.
Tajitsu and his team used Japan’s Subaru Telescope on the summit of Mauna Kea, Hawaii. Its lofty altitude, large aperture and high sensitivity allowed the team to examine the composition of the material expelled from V339 Del at four points after the explosion. During the first three epochs, they were able to identify a significant quantity of Be-7 ejected from the nova at a high velocity.
By the end of their observations, however, no beryllium was visible; the team is still investigating the reason behind the complete disappearance. Continuing studies of V339 Del may help answer lingering questions such as this.
Beryllium-7 has a half-life of 53 days. Every eight weeks or so, the amount of beryllium is reduced by half as it decays into lithium-7, which is even more difficult to detect. In order to observe the rapidly shifting beryllium before it transitions into lithium, scientists must observe the new nova quickly, which can create scheduling challenges with large telescopes.
By studying lithium in the galaxy, scientists can understand how it evolves chemically over time.
“In general, all the chemical elements play an important role in galactic evolution, because they determine the chemical composition of the galactic gas from which stars form,” Hernanz said.
“The study of the so-called chemical evolution of the galaxy determines how this chemical composition evolves along the history of the galaxy.”
Tajitsu and his team hope to repeat their observations for many other classical novae, confirming how they might contribute to the evolution of lithium in the current universe.
Other than the first detection of beryllium-7, V339 Del has nothing to make it stand out from other novae. It appears to be a typical explosion on a carbon and oxygen dwarf. This means that classical novae could easily contribute a substantial amount of lithium to the galaxy.
The research, along with Hernanz’s accompanying News & Views article, was published online today (Feb. 18) in the journal Nature.
The steady glow of high-energy gamma-ray light that spreads across the cosmos has puzzled astronomers for decades. One team of researchers thinks it has the best explanation yet for the source of this strange emission.
After observing the universe with NASA’s Fermi Gamma-ray Space Telescope for six years, scientists with the mission say the majority of the gamma-ray glow they have seen can be explained by objects already known to science. If there are any as-yet unknown sources out there, their contribution to the glow would be very small, scientists say.
“We have a very plausible story. We’re not 100 percent confident that this is the final answer, but it really constrains what other exotic possibilities could be out there,” said Keith Bechtol, a postdoctoral researcher at the University of Chicago and a member of the Fermi collaboration who worked on the analysis.
NASA’s Fermi Gamma-ray Space Telescope snaps pictures of the entire observable universe — from end to end — in gamma-rays, which are some of the highest-energy photons in nature.
While that wide view of the universe is useful, it can make it a challenge to pinpoint the exact sources of these gamma-rays. Instead, Fermi sees a diffuse glow coming from the universe. This glow is technically known as the extragalactic gamma ray background, or the EGB. Previous gamma-ray telescopes have also seen this light that fills the background of the cosmos.
“We’ve known about this gamma-ray background since the late 1960s,” Bechtol said. “It’s a very-long-standing mystery, and each generation of gamma-ray telescopes has given us a little more information.”
With help from other telescopes, the Fermi telescope can identify where some of this high-energy background light is coming from. There are very energetic galaxies called blazars, for example, that give off a high flux of gamma-rays. The Energetic Gamma Ray Experiment Telescope (EGRET), which preceded Fermi, broke records by detecting some 300 gamma-ray sources. So far, the Fermi telescope has identified more than 3,000 sources.
But 3,000 is only a drop in the ocean of gamma-ray sources in the entire universe, scientists say. [Top 10 Gamma-Ray Sources in the Universe]
“We think every galaxy is producing gamma-rays at some level,” Bechtol said. “The vast majority are too faint to be seen individually and instead their collective emission is blurred together.” (Many galaxies radiate high levels of optical light, and can be seen by telescopes like the Hubble. But their gamma-ray emission is too faint to be detected.)
“It’s frustrating not to know the answer, but the fact that there’s a mystery — I think that’s what attracted a lot of us to this problem,” Bechtol said. “At least for me, I like being on the edge of that discovery space where there’s still blank parts on the map.”
The Fermi telescope can’t see most of the objects that radiate gamma-ray light, so the scientists have to try to estimate how many gamma-ray objects are out there.
In an analysis first made public in September 2014, members of the Fermi collaboration took the known sources of gamma-rays and added them together with models that predicted the frequency and location of unseen sources. The scientists calculated how much gamma-ray light both the detected and modeled sources would produce together.
This calculated output of gamma rays matches closely with the actual gamma ray-background that Fermi observes — the entire EGB.
The final estimate shows that roughly 50 percent of the gamma-ray background comes from extremely energetic galaxies known as blazars. Ten to 30 percent of the gamma ray background emanates from star-forming galaxies like the Milky Way, which can collectively contain many smaller gamma-ray sources, like supernovas. Another 20 percent is from radio galaxies, which are blazars, but are pointed away from the Earth, and thus cannot be seen as easily by Fermi.
“There could definitely be new gamma-ray sources out there,” Bechtol said. “It’s just that their total contribution would have to be relatively small.”
It’s also possible that dark matter — the mysterious material that makes up 80 percent of all the matter in the universe — is producing gamma-rays, and the Fermi results may help scientists figure out what kind of particle (or particles) make up dark matter.
Two large uncertainties remain in Fermi’s estimation. First, it is difficult to measure the gamma-ray glow of the universe to begin with, and Bechtol said he and his collaborators put a lot of time into improving that measurement.
Second, the scientists are making estimates about objects they cannot directly observe, most of which are located beyond the Milky Way galaxy (or extragalactic).
“When [scientists] first discovered the gamma-ray background, it was largely a mystery as to what created it,” Bechtol said. “And now it seems like everything is fitting together very well. Right now, the simplest explanation involving known astrophysical sources seems to be doing just fine.”
Light from back in time
Fermi’s success at decoding the gamma-ray background had depended largely on its increased sensitivity to gamma-rays and its detection of more gamma-ray sources than previous telescopes. In addition, Fermi scientists have worked to gain a better understanding of how gamma-ray emissions have changed throughout the history of the universe. This is valuable because when Fermi looks at sources of gamma-rays, it is actually looking into the past.
Light travels at a finite speed — the light from the sun takes 8 minutes to reach Earth, which means humans actually see the sun as it was 8 minutes ago. By the same logic, objects that are billions of light-years away from Earth are seen by Fermi as they were billions of years ago.
“We’re literally measuring the light output over the history of the universe, and for me, that’s what makes this exciting,” Bechtol said. “We’re seeing all different time periods in the universe at the same time. All of the light from all those different periods is added together to form the gamma ray background.”
Having a historical perspective makes a big difference for Fermi because the cosmic output of gamma-rays has likely been different at various times throughout the last 13 billion years. For example, the universe has seen periods when the population of blazars exploded and other times when the population growth slowed down. They also need to understand precisely how far away those blazars are, in order to accurately measure how long ago these bright sources burned.
The Fermi scientists have solved a long-standing puzzle, but Bechtol said there are still other mysteries in the gamma-ray universe. There are other gamma-ray telescopes that can detect even higher-energy gamma-rays than Fermi, and it’s possible that in those energy ranges, there are sources of gamma-rays that scientists don’t know about yet.
“We think this [result] is converging on the final answer, but history has shown us that, sometimes, there’s more to the story,” Bechtol said. “I certainly think that, as we start to look at higher energies […], there will start to be some surprises.”
One of the least likely places you might think astronomers would learn about ancient supernovae is at the bottom of the ocean, but in new research scientists have done just that.
Through the careful analysis of ocean sediment, tiny particles that originated from deep space have settled on the seabed, locking the chemical secrets to supernova processes that would have otherwise remained a mystery.
“Small amounts of debris from these distant explosions fall on the Earth as it travels through the galaxy,” said lead researcher Anton Wallner, of the Australian National University. “We’ve analyzed galactic dust from the last 25 million years that has settled on the ocean and found there is much less of the heavy elements such as plutonium and uranium than we expected.”
Supernovas are powerful explosions triggered when massive stars reach the ends of their lives. During these powerful events, many elements are forged, including elements that are essential for life to thrive — such as iron, potassium and iodine.
However, as pointed out by an Australian National University press release, even heavier elements like lead, gold and radioactive elements like uranium and plutonium can be created. But it appears that the formation processes for the heaviest elements are at odds with current astrophysical theory.
Wallner and his team studied samples of sediment from the bottom of a stable area at the bottom of the Pacific Ocean. But when measuring the quantities of plutonium-244, a radioisotope that is produced by supernovae, they found something strange in their results — there was 100 time less plutonium-244 than predicted.
Plutonium-244 has a half-life of 81 million years, making it an excellent indicator of the number of supernovae that have exploded nearby in recent galactic history. “So any plutonium-244 that we find on earth must have been created in explosive events that have occurred more recently, in the last few hundred million years,” said Wallner.
But the fact that there is less recent deposition of the heaviest of elements, despite the fact that we know supernovae have erupted nearby, suggests a different formation mechanism may be responsible for plutonium-244 and elements like it.
“It seems that these heaviest elements may not be formed in standard supernovae after all,” concludes Wallner. “It may require rarer and more explosive events such as the merging of two neutron stars to make them.”
This research has been published in Nature Communications.
The white spot on Ceres in a series of new photos taken on Jan. 13 by NASA’s Dawn spacecraft, which is rapidly approaching the round dwarf planet in the asteroid belt between the orbits of Mars and Jupiter. But when the initial photo release on Monday (Jan. 19), the Dawn scientists gave no indication of what the white dot might be.
“Yes, we can confirm that it is something on Ceres that reflects more sunlight, but what that is remains a mystery,” Marc Rayman, mission director and chief engineer for the Dawn mission, told Space.com in an email.
The new images show areas of light and dark on the face of Ceres, which indicate surface features like craters. But at the moment, none of the specific features can be resolved, including the white spot.
“We do not know what the white spot is, but it’s certainly intriguing,” Rayman said. “In fact, it makes you want to send a spacecraft there to find out, and of course that is exactly what we are doing! So as Dawn brings Ceres into sharper focus, we will be able to see with exquisite detail what [the white spot] is.”
Ceres is a unique object in our solar system. It is the largest object in the asteroid belt and is classified as an asteroid. It is simultaneously classified as a dwarf planet, and at 590 miles across (950 kilometers, or about the size of Texas), Ceres is the smallest known dwarf planet in the solar system.
The $466 million Dawn spacecraft is set to enter into orbit around Ceres on March 6. Dawn left Earth in 2007 and in the summer of 2011, it made a year-long pit stop at the asteroid Vesta, the second largest object in the asteroid belt.
While Vesta shared many properties with our solar system’s inner planets, scientists with the Dawn mission suspect that Ceres has more in common with the outer most planets. 25 percent of Ceres’ mass is thought to be composed of water, which would mean the space rock contains even more fresh water than Earth. Scientists have observed water vapor plumes erupting off the surface of Ceres, which may erupt from volcano-like ice geysers.
The mysterious white spot captured by the Dawn probe is one more curious feature of this already intriguing object.
Scientists have detected the origins of three bright gamma-ray signals from objects beyond our own Milky Way galaxy for the first time, including one signal from a strange “superbubble” of gas.
The gamma-ray signals from three very different astronomical objects were detected in the Large Magellanic Cloud (LMC) — the biggest satellite galaxy of the Milky Way — by a telescope network in Africa. They are spewing high-energy gamma-rays and are giving the Milky Way a run for its money.
Two of the newfound gamma-ray sources, a pulsar wind nebula and a supernova remnant, are far more powerful than similar sources in the Milky Way. The third object, the so-called superbubble, is an entirely new source of gamma-rays in space, the researchers said.
“Some people may say that discovering three sources in an external galaxy is not such a big deal —but for gamma-ray astronomy, this is a major step forward,” study co-author Stefan Ohm of DESY, a national research center in Germany, said on behalf of the research team. [Top 10 Gamma-Ray Sources in the Universe]
Gamma-rays from the great beyond
When gamma-rays slam into Earth’s upper atmosphere, they emit a faint, blue light. Astronomers can then use this brief burst of light to trace the rays back to some of the most violent phenomena in the universe, including winds streaming off of pulsars and supernova remnants.
In the new study, researchers used the High Energy Stereoscopic System (HESS) — four 13-meter (43 feet) telescopes in Namibia, Africa — to observe the largest star-forming region within the LMC. Over the course of 210 hours, the images lit up with a faint blue light, every photon revealing a single gamma-ray, traceable back to three distinct sources in the LMC.
“So far, we only knew individual sources in the Milky Way, or observed emission from entire galaxies,” Ohm told Space.com in an email. “This is the first time that we discovered more than just one stellar-type gamma-ray source in an external galaxy.”
All three sources are related to supernovas, the dramatic explosions of massive stars ending their lives. When a supernova explodes, the outer layers of the expanding material crash into nearby gas and dust, driving a tremendous shock wave. Electrons and other charged particles, accelerated in the rapidly expanding wave, emit gamma-rays.
The first source, PSR J0537-6910, is a pulsar — the dense, rapidly spinning remnant of a supernova explosion. Its wind nebula emits far more gamma-rays than its Milky Way counterpart, the Crab Nebula. One of the most studied celestial objects, the Crab Nebula used to hold the record as the brightest high-energy source in the sky. This newly discovered object, however, outshines the Crab Nebula by an order of magnitude.
The second source, a supernova remnant known as N132D, also appears to be another record breaker. But this one was a surprise. Although supernova remnants are known to emit gamma-rays, astronomers expect it to be much easier when the remnants are younger. If they’re too old, the supernova fronts will have slowed down so much that they’re no longer able to efficiently accelerate particles. [The Gamma-Ray Universe Revealed (Gallery)]
The gamma-ray source N132D is between 2,500 and 6,000 years old. It’s considered a middle-age supernova remnant and yet is brighter than any of its galactic counterparts. On the same note, the researchers were surprised that they didn’t detect the supernova remnant SN 1987A, which is the youngest supernova remnant in the local group of galaxies.
But the most interesting source, scientists say, is the superbubble 30 Dor C, a massive shell of gas. Until now, astronomers had never seen gamma-rays of any kind from a superbubble object.
“We are quite confident that these energetic particles are powered by supernova explosions, and probably a large part derives its energy from the fast-expanding shells created by these supernovas,” Ohm said. “However, according to our current knowledge, these supernova shells do not have the right properties to accelerate particles to the very highest energies required. The shells are too small to do so.”
But 30 Dor C is far from small. Its cavity expands 270 light-years across and is thought to have been carved by multiple supernovas and strong stellar winds. It’s now the first of its kind to be a known source of gamma-rays, and astronomers are fairly certain its large size is the culprit.
The LMC’s supernova rate relative to its stellar mass is five times that of our galaxy. The researchers think that its quick ability to turn over stars has likely caused it to breed so many extreme objects.
Astronomers hope that high-energy gamma-rays will help them better understand cosmic rays, charged particles that whiz throughout the cosmos. The problem is that researchers still don’t know where these particles, which are mostly protons stripped from hydrogen atoms, receive their energy boost.
Because cosmic rays are charged, they feel the push and pull of any magnetic field they come across in space. So, by the time they reach the Earth, they’re hitting it from all vantage points. But cosmic rays produce gamma-rays, which don’t have this problem, so astronomers can use gamma-rays to probe likely sites of cosmic-ray acceleration.
They’ve already linked cosmic rays to supernovas, but these results provide the first observational hint that superbubbles might also be a source of cosmic rays, Ohm said. A better understanding of the origins of gamma-rays and cosmic rays will further shed light on the dramatic stellar explosions across the galaxy and beyond.
Scientists saw repeating pulses from a quasar — a bright galactic core powered by at least one huge black hole — and say the light is likely being generated during the latter stages of a monster black hole collision.
If this interpretation is correct, researchers could learn a great deal more about the final phases of such mergers, where simulations tend to break down — a situation dubbed “the final parsec problem.”
The light signal from 3.5 billion light-years away was spotted by the Catalina Real-Time Transient Survey (CRTS), a set of three telescopes in Australia and the United States that look at 500 million light sources across 80 percent of the sky observable from Earth.
“There has never been a data set on quasar variability that approaches this scope before,” lead study author George Djorgovski, director of the Center for Data-Driven Discovery at the California Institute of Technology, said in a statement.
“In the past, scientists who study the variability of quasars might only be able to follow some tens — or, at most, hundreds — of objects with a limited number of measurements,” Djorgovski said in the statement. “In this case, we looked at a quarter-million quasars, and were able to gather a few hundred data points for each one.”
The discovery came as a surprise, as the researchers were originally trying to learn more about how quasar brightness varies. While scrutinizing the data, however, they found 20 quasars that varied predictably — unlike the chaotic signals that researchers are used to.
Further analysis showed that one quasar, called PG 1302-102, likely has two black holes separated by just a few hundredths of a light-year. Other mergers observed previously placed such colliding black holes much further apart — anywhere between tens and thousands of light-years.
To verify the signal, which appears to repeat every five years, researchers brought in historical information covering most of the last two decades. Also, the light spectrum revealed something interesting happening in the gases surrounding the disc, which are spinning so quickly that they get superheated.
“When you look at the emission lines in a spectrum from an object, what you’re really seeing is information about speed — whether something is moving toward you or away from you and how fast. It’s the Doppler effect,” said co-author Eilat Glikman, an assistant professor of physics at Middlebury College in Vermont.
With quasars, you typically have one emission line, and that line is a symmetric curve,” Glikman added. “But with this quasar, it was necessary to add a second emission line with a slightly different speed than the first one in order to fit the data. That suggests something else, such as a second black hole, is perturbing this system.”
Researchers aren’t sure what is causing the repeating light signal, but possibilities could include jets of material rotating around the center, similar to a lighthouse, or a distorted disc of material around the black holes that is either throwing material on the black holes or “blocking light from the quasar at regular intervals,” Glikman said.