Latest news with #EinsteinProbe
Yahoo
20-02-2025
- Science
- Yahoo
'Impossible' pair of vampire stars discovered by Einstein Probe's X-ray vision
When you buy through links on our articles, Future and its syndication partners may earn a commission. A flash of powerful X-ray light coming from a nova explosion on a white dwarf star has caught the attention of astronomers using the Chinese–European Einstein Probe. This nova is especially exciting because the white dwarf star on which it is found exists in a particularly unusual binary star system. The high-energy flare was spotted on May 27, 2024 coming from a star system in the Small Magellanic Cloud (SMC), which is a neighboring satellite of our Milky Way galaxy. "We were chasing fleeting sources, when we came across this new spot of X-ray light in the SMC," said Alessio Marino of the Institute of Space Sciences in Spain in a statement. "We realized that we were looking at something unusual, [something] that only Einstein Probe could catch." The Einstein Probe was launched in January 2024 to study the high-energy universe, and among its instruments is its Wide-field X-ray Telescope (WXT), which is the only X-ray telescope currently in orbit that can detect lower-energy X-rays with enough sensitivity to pinpoint their sources. And, in this case, the source was a bizarre pairing of stars. One of the stars is quite massive, totaling about 12 times the mass of our sun. It's called a "Be" star, meaning that it is of spectral type B (the second hottest type of main sequence star) and that it exhibits strong spectral emission lines. Its companion is a white dwarf star that is about 20% more massive than our sun. White dwarfs are the final stage of sun-like stars that have expelled their outer layers to uncover their cores. It's in this dichotomy between the two objects that a stellar paradox lies. A sun-like star can survive for at least hundreds of millions of years, or in the actual sun's case, billions of years, before it becomes a white dwarf. Yet, a star of 12 solar masses should explode as a supernova after just 20 million years. So, given the huge difference in lifespans, how can this Be star find itself co-orbiting with a white dwarf companion? The solution seems to be that the Be star and the white dwarf are sharing material, taking turns feeding off one another like vampires. Originally, scientists believe, the system probably contained two stars with masses six and eight times the mass of our sun, respectively. The more massive a star is, the faster it uses up its fuel for nuclear fusion reactions in its core, and the shorter its lifespan is. So, it would have been the eight-solar-mass star that reached this point first. As the fusion reactions in its core began to stutter, the radiation pressure of the energy produced in those reactions began to drop off. This energy holds a star up against the inward pull of its own gravity, and when this radiation stream weakens it leads to gravity making the outer layers around the core more compact, raising temperatures so that fusion reaction could sporadically ignite in the star's outer layers. This would have led to pulsations that reverberated through the star, puffing up its outer extremities so that it became a giant. At this point, the giant eight-solar-mass star's outer layers would have become vulnerable to being stolen by the gravity of the less massive star. At the time, the two stars would have only been a few million miles apart, orbiting each other once every three days. This proximity should have allowed the gravity of the less massive star to begin stealing material from the more massive star, whittling it down. Eventually, the six-solar-mass star would have grown to 12 solar masses, while all that was left of the eight-solar-mass star was its core: a white dwarf 1.23 times the mass of our sun. Now, the more compact white dwarf is returning the favor, its gravity stealing back loosely held material from the 12-solar-mass star. As this material streams back onto the white dwarf, the pressure and temperature at the point of accretion on the white dwarf's surface grows, until a localized thermonuclear explosion erupts. This results in a nova, or a brilliant outburst of light, including X-rays. That's what Einstein Probe saw. "This study gives us new insights into a rarely observed phase of stellar evolution, which is the result of a complex exchange of material that must have happened among the two stars," said Ashley Chrimes of the European Space Agency, in the statement. "It's fascinating to see how an interacting pair of massive stars can produce such an intriguing outcome." The exchange of material has also altered the fates of the two stellar objects. Ordinarily, a six-solar-mass star would reach the end of its life by swelling into a red giant, before casting away its outer layers to leave behind a white dwarf. But by having accreted so much mass from its companion, it becomes destined to explode as a supernova. Related Stories: — Astronomers unsure what caused 'weird explosion' seen by Einstein Probe's X-ray eye — China's Einstein Probe already making discoveries during commissioning phase — What was the mysterious space signal scientists discovered in 2024? Here are some possibilities Meanwhile an eight-solar-mass star is right on the borderline between stars that evolve into red giants and stars that go supernova — but this one has instead turned into a white dwarf that's more typical of less massive stars. That's not to say it won't eventually go supernova. Type Ia supernova explosions spur the destruction of white dwarf stars that have accreted too much mass. The limit is 1.44 times the mass of our sun; it won't take too much accretion to push this white dwarf over the edge so that it obliterates itself in a supernova. Its only chance to survive relies on its 12-solar-mass companion exploding first. It's now a race against time to see which of the companions survives the longest. The findings were published on Feb. 18 in The Astrophysical Journal Letters.
Yahoo
20-02-2025
- Science
- Yahoo
'Impossible' pair of vampire stars discovered by Einstein Probe's X-ray vision
When you buy through links on our articles, Future and its syndication partners may earn a commission. A flash of powerful X-ray light coming from a nova explosion on a white dwarf star has caught the attention of astronomers using the Chinese–European Einstein Probe. This nova is especially exciting because the white dwarf star on which it is found exists in a particularly unusual binary star system. The high-energy flare was spotted on May 27, 2024 coming from a star system in the Small Magellanic Cloud (SMC), which is a neighboring satellite of our Milky Way galaxy. "We were chasing fleeting sources, when we came across this new spot of X-ray light in the SMC," said Alessio Marino of the Institute of Space Sciences in Spain in a statement. "We realized that we were looking at something unusual, [something] that only Einstein Probe could catch." The Einstein Probe was launched in January 2024 to study the high-energy universe, and among its instruments is its Wide-field X-ray Telescope (WXT), which is the only X-ray telescope currently in orbit that can detect lower-energy X-rays with enough sensitivity to pinpoint their sources. And, in this case, the source was a bizarre pairing of stars. One of the stars is quite massive, totaling about 12 times the mass of our sun. It's called a "Be" star, meaning that it is of spectral type B (the second hottest type of main sequence star) and that it exhibits strong spectral emission lines. Its companion is a white dwarf star that is about 20% more massive than our sun. White dwarfs are the final stage of sun-like stars that have expelled their outer layers to uncover their cores. It's in this dichotomy between the two objects that a stellar paradox lies. A sun-like star can survive for at least hundreds of millions of years, or in the actual sun's case, billions of years, before it becomes a white dwarf. Yet, a star of 12 solar masses should explode as a supernova after just 20 million years. So, given the huge difference in lifespans, how can this Be star find itself co-orbiting with a white dwarf companion? The solution seems to be that the Be star and the white dwarf are sharing material, taking turns feeding off one another like vampires. Originally, scientists believe, the system probably contained two stars with masses six and eight times the mass of our sun, respectively. The more massive a star is, the faster it uses up its fuel for nuclear fusion reactions in its core, and the shorter its lifespan is. So, it would have been the eight-solar-mass star that reached this point first. As the fusion reactions in its core began to stutter, the radiation pressure of the energy produced in those reactions began to drop off. This energy holds a star up against the inward pull of its own gravity, and when this radiation stream weakens it leads to gravity making the outer layers around the core more compact, raising temperatures so that fusion reaction could sporadically ignite in the star's outer layers. This would have led to pulsations that reverberated through the star, puffing up its outer extremities so that it became a giant. At this point, the giant eight-solar-mass star's outer layers would have become vulnerable to being stolen by the gravity of the less massive star. At the time, the two stars would have only been a few million miles apart, orbiting each other once every three days. This proximity should have allowed the gravity of the less massive star to begin stealing material from the more massive star, whittling it down. Eventually, the six-solar-mass star would have grown to 12 solar masses, while all that was left of the eight-solar-mass star was its core: a white dwarf 1.23 times the mass of our sun. Now, the more compact white dwarf is returning the favor, its gravity stealing back loosely held material from the 12-solar-mass star. As this material streams back onto the white dwarf, the pressure and temperature at the point of accretion on the white dwarf's surface grows, until a localized thermonuclear explosion erupts. This results in a nova, or a brilliant outburst of light, including X-rays. That's what Einstein Probe saw. "This study gives us new insights into a rarely observed phase of stellar evolution, which is the result of a complex exchange of material that must have happened among the two stars," said Ashley Chrimes of the European Space Agency, in the statement. "It's fascinating to see how an interacting pair of massive stars can produce such an intriguing outcome." The exchange of material has also altered the fates of the two stellar objects. Ordinarily, a six-solar-mass star would reach the end of its life by swelling into a red giant, before casting away its outer layers to leave behind a white dwarf. But by having accreted so much mass from its companion, it becomes destined to explode as a supernova. Related Stories: — Astronomers unsure what caused 'weird explosion' seen by Einstein Probe's X-ray eye — China's Einstein Probe already making discoveries during commissioning phase — What was the mysterious space signal scientists discovered in 2024? Here are some possibilities Meanwhile an eight-solar-mass star is right on the borderline between stars that evolve into red giants and stars that go supernova — but this one has instead turned into a white dwarf that's more typical of less massive stars. That's not to say it won't eventually go supernova. Type Ia supernova explosions spur the destruction of white dwarf stars that have accreted too much mass. The limit is 1.44 times the mass of our sun; it won't take too much accretion to push this white dwarf over the edge so that it obliterates itself in a supernova. Its only chance to survive relies on its 12-solar-mass companion exploding first. It's now a race against time to see which of the companions survives the longest. The findings were published on Feb. 18 in The Astrophysical Journal Letters.
Yahoo
11-02-2025
- Science
- Yahoo
What was the mysterious space signal scientists discovered in 2024? Here are some possibilities
When you buy through links on our articles, Future and its syndication partners may earn a commission. Having launched on January 9, 2024 by the Chinese Academy of Sciences, the Einstein Probe detected several new events during its commissioning phase. Last October, Yuan Weimin, the spacecraft's principle investigator, told China Central Television that the X-ray observatory had already discovered around 60 very strong transient celestial objects, close to a thousand potential transients, and nearly 500 stellar flares, along with a gamma-ray burst from the very early universe. One of those detections was EP240408a, an unusual blast that lit up discussions between astronomers. Zhang and his colleagues immediately utilized the spacecraft's second instrument, the Follow-up X-ray Telescope, to take observations of the new source 1.8 days after it was first spotted by its companion, the Wide-field X-ray Telescope. Both teams of researchers sprung into action, requesting time on Earth- and space-based instruments in a multitude of wavelengths. Together, the two research groups pointed almost 20 different telescopes besides the Einstein Probe at the new incident, spanning optical, radio, gamma ray, ultraviolet and near-infrared wavelengths. Most of those instruments saw nothing. And that's unusual. Known X-ray emitters tend to be of the multiwavelength sort, sending out signals in more than one regime. Zhang and his colleagues only saw the EP240408a shine in the X-ray, while O'Connor identified a possible optical counterpart: a small, faint galaxy that may be where the signal emerged. That's not the only way that EP240408a doesn't fit with the existing transient models. The new explosion lit up X-rays for somewhere between seven and 23 days, an estimate based on when EP was pointed in its direction. Fast X-ray bursts, intense short explosions resulting from violent processes, flare anywhere from sub-seconds to hundreds of seconds before they disappear. Longer transients associated with galactic nuclei last anywhere from months to years. The unusual mid-range sets EP240408a apart. Additionally, the new target fired off a 12-second flare 300 times brighter than the underlying X-ray emission before fading to the lower levels. NASA's Neutron star Interior Composition Explorer (NICER) was one of the few instruments able to catch a glimpse of EP's newest hit. "Once we realized that EP240408a was a compelling new transient, we requested NICER pointings," Francesco Zelati, a researcher at the Institute of Space Sciences and part of the Zhang group, told by email. Zelati and his colleagues used the International Space Station-based X-ray observatory to better characterize the new event's X-ray properties and capture any rapid changes in its emission. NICER was one of the few instruments able to detect the brief event both because of its high collecting area and its flexible scheduling. "Many other observatories either lack the rapid scheduling or the sensitivity in the relevant energy ranges," Zelati said. NICER's quick response allowed it to obtain data that was "key to track the evolution of the transient," he said. Both teams also relied on detection by NASA's Neil Gehrels Swift Observatory (Swift) in the X-ray. In addition to measuring the signal, Zhang said that the spacecraft helped to narrow down the location of the source. O'Connor used Swift's measure of hydrogen, the primordial gas that is the building material for everything in the universe, to determine that the explosion came from outside the Milky Way. Their findings led them to infer hydrogen is absorbing the X-ray photons in the far-off host galaxy. Both teams turned a variety of optical telescopes towards the flare. With the Gemini South Observatory, based in Chile, O'Connor identified a faint galaxy that could be home to the event. The two independent teams of astronomers compared their measurements and came to slightly different conclusions. O'Connor and his colleagues suspect that the distant explosion may be an event known as a tidal disruption event, or TDE. A TDE occurs when a star passes dangerously close to a black hole and is shredded by its gravitational forces. Only a hundred TDEs have been discovered since the first was spotted in 1995. In extremely rare cases, the black hole's tidal forces fire material outward in a high-velocity jet that interacts with nearby material, shining brightly in both X-ray and radio wavelengths. Only four TDEs to date are thought to have relativistic jets — and the X-ray signal is very similar to those four. But observations in radio frequencies with multiple telescopes have come up empty. To Zhang, that omits jetted TDEs from consideration. "It is hard to explain EP240408a with jet [TDE] due to the lack of low-frequency — radio to near-infrared — radiation of the source," he said. His coauthor, Zelati, isn't so quick to dismiss the results. It's possible that radio or longer-wavelength emission would appear later, when the jet expands into the surrounding medium. "This radio-bright phase could emerge anywhere from weeks to many months after the initial event," he said. O'Connor and his colleagues had the same thought. They suspect that the jet may take some time to decelerate, delaying the shockwave that would spark radio emissions. "Such delayed late time radio emission has been observed in many past TDEs recently over a range of timescales," he said. "It appears to be an almost ubiquitous property." It's the timescale that is a challenge to explain, he said. While EP240408a has a similar appearance to other relativistic jetted TDEs, the X-ray signal decays more rapidly. "Such a short timescale can be possible if the black hole is quite small and the star quite dense," O'Connor says. "We favored an intermediate mass black hole disrupting a white dwarf." Zhang and colleagues suspect that the unusual signal may instead be an entirely new class of object. "We suggest that EP240408a may represent a new type of transients with intermediate timescales of the order of about 10 days, that may have been missed in previous time-domain surveys," they wrote in their paper. That could be because intermediate-length X-ray transients could go unnoticed in surveys focusing on either very long-scale objects or extremely short bursts, Zelati said. O'Connor and his coauthors don't rule out a brand new class of object. Pointing out in their research that the observed properties of EP240408a "do not directly align with any known transient class," they admit that a jetted TDE does not perfectly explain the observations. "The alternative is that EP240408a may represent a new, previously unknown class of transient," they wrote. Related Stories: — X-rays reveal secret gas in huge and distant galaxy cluster — X-ray spacecraft reveals odd 'Cloverleaf' radio circle in new light (image) — Record-breaking radio burst could help us find the universe's missing matter "Discovering a new class of intermediate X-ray transients like EP240408a would significantly enhance our comprehension of the diverse and dynamic processes in the universe," Zelati said. Such a discovery would fill in gaps of classifications of X-ray phenomena, potentially leading to the development of new theories and observational studies to find more like it. "Ultimately, it would broaden our understanding of high-energy astrophysical events," he said. It's extremely likely that the Einstein Probe will most likely detect similar events throughout its mission, assuming it hasn't already. "Future detections of similar events by EP will help us figure this out as a community," O'Connor wrote. "I am definitely looking forward to the weird transients EP will discover in the future!"
Yahoo
11-02-2025
- Science
- Yahoo
A Strange New Cosmic Explosion May Have Just Been Discovered
A bizarre cosmic explosion has puzzled astronomers. It's either a very rare case of the stars aligning just right (literally) – or something powerful never seen before. The event is designated EP240408a, as it was first detected by the Einstein Probe, an X-ray space telescope, on 8 April 2024. At a glance, it appeared to be a run-of-the-mill gamma ray burst, which typically emits bright X-rays too. But when an all-star cast of telescopes observed it in a range of wavelengths, including ultraviolet, optical, near-infrared, radio, X-rays, and gamma rays, they found that it didn't quite match any particular known type of event. The current leading explanation, according to a new study, is that it's the death throes of a white dwarf being torn apart by a medium-sized black hole. This created a high-speed jet of material that, as luck would have it, is pointing directly at Earth. "EP240408a ticks some of the boxes for several different kinds of phenomena, but it doesn't tick all the boxes for anything," says Brendan O'Connor, astronomer at Carnegie Mellon University and lead author of the study. "In particular, the short duration and high luminosity are hard to explain in other scenarios. The alternative is that we are seeing something entirely new!" The Universe is ablaze with transient events – energetic flashes caused by outbursts from stars and black holes, stars exploding as supernovae, stars being devoured by black holes, and all kinds of other cosmic drama. Astronomers can figure out what each event is by its duration, frequency, source, and the specific combination of wavelengths it emits. After its discovery by the Einstein Probe, EP240408a was observed by a squad of other ground- and space-based telescopes, including the Nuclear Spectroscopic Telescope Array (NuSTAR), Swift, Gemini, Keck, the Dark Energy Camera (DECam), the Very Large Array (VLA), the Australia Telescope Compact Array (ATCA), and the Neutron star Interior Composition Explorer (NICER). Armed with this data, astronomers pieced together the event's properties – but that only deepened the mystery. EP240408a flared up in soft X-rays for the first 10 seconds, plateaued at a steady glow for about four days, then faded quickly within another day. That's much longer than most gamma-ray bursts, which last up to several hours, but not long enough to fit into other known categories. Its brightness in X-rays was in a similar reverse-Goldilocks zone: too bright for some phenomena and not bright enough for others. Weirdest of all, the VLA saw no sign of radio emission from the source when it checked 11 days, 158 days, and 258 days after the initial flare-up. "When we see something this bright for this long in X-rays, it usually has an extremely luminous radio counterpart," says O'Connor. "And here we see nothing, which is very peculiar." After ruling out several possible explanations, such as quasars or the mysterious fast blue optical transients, the astronomers put forward the most likely culprit: a tidal disruption event (TDE). These are flashes of light thrown off when black holes messily gobble up stars. In rare cases, TDEs produce huge jets of material that blast off from the black hole's poles. These can, by chance, point straight towards Earth, which produces the signature seen. The characteristics of the signal suggest that specifically, it was an intermediate-mass black hole chowing down on a white dwarf star. The thing is, there should still be some radio emissions from a jetted TDE. The team's hypothesis for why none have been found so far is that the event was caught too early – previous research suggests that it can take hundreds or even thousands of days for jet material to slow down enough to begin beaming radio signals. If future observations do detect radio emissions, this could close the case on EP240408a. But if it stays silent, it could mean it's a particularly weird gamma-ray burst – or perhaps a brand new type of transient. The research was published in The Astrophysical Journal Letters. Astronomers Amazed by Perfect 'Einstein Ring' Gleaming in Space Astronomers Capture Breathtaking Image of Newborn Star Taking Shape The Risk of Space Junk Hitting Planes Is Rising in The Era of SpaceX
