Space & Astronomy

Subterms

    More stories

    • 125 Shares189 Views

      in Space & Astronomy

      How massive stars in binary systems turn into carbon factories

      by

      The next time you thank your lucky stars, you might want to bless the binaries. New calculations indicate that a massive star whose outer layer gets torn off by a companion star ends up shedding a lot more carbon than if the star had been born a loner.

      “That star is making about twice as much carbon as a single star would make,” says Rob Farmer, an astrophysicist at the Max Planck Institute for Astrophysics in Garching, Germany.

      All life on Earth is based on carbon, the fourth most abundant element in the cosmos, after hydrogen, helium and oxygen. Like nearly every chemical element heavier than helium, carbon is formed in stars (SN: 2/12/21). For many elements, astronomers have been able to pin down the main source. For example, oxygen comes almost entirely from massive stars, most of which explode, while nitrogen is made mostly in lower-mass stars, which don’t explode. In contrast, carbon arises both in massive and lower-mass stars. Astronomers would like to know exactly which types of stars forged the lion’s share of this vital element.

      Farmer and his colleagues looked specifically at massive stars, which are at least eight times heavier than the sun, and calculated how they behave with and without partners. Nuclear reactions at the core of a massive star first turn hydrogen into helium. When the core runs out of hydrogen, the star expands, and soon the core starts converting helium into carbon.

      Sign Up For the Latest from Science News

      Headlines and summaries of the latest Science News articles, delivered to your inbox

      Thank you for signing up!

      There was a problem signing you up.

      But massive stars usually have companion stars, adding a twist to the storyline: When the star expands, the companion’s gravity can tear off the larger star’s outer envelope, exposing the helium core. That allows freshly minted carbon to stream into space via a flow of particles.

      “In these very massive stars, these winds are quite strong,” Farmer says. For instance, his team’s calculations indicate that the wind of a star born 40 times as massive as the sun with a close companion ejects 1.1 solar masses of carbon before dying. In comparison, a single star born with the same mass ejects just 0.2 solar masses worth of carbon, the researchers report in a paper submitted to arXiv.org October 8 and in press at the Astrophysical Journal.

      If the massive star then explodes, it also can outperform a supernova from a solo massive star. That’s because, when the companion star removes the massive star’s envelope, the helium core shrinks. This contraction leaves some carbon behind, outside the core. As a result, nuclear reactions can’t convert that carbon into heavier elements such as oxygen, leaving more carbon to be cast  into space by the explosion. Had the star been single, the core would have destroyed much of that carbon.

      By analyzing the output from massive stars of different masses, Farmer’s team concludes that the average massive star in a binary ejects 1.4 to 2.6 times as much carbon through winds and supernova explosions as the average massive star that’s single.

      Given how many massive stars are in binaries, astronomer Stan Woosley says emphasizing binary-star evolution, as the researchers have done, is helpful in pinning down the origin of a crucial element. But “I think they are making too strong a claim based on models that may be sensitive to uncertain physics,” says Woosley, of the University of California, Santa Cruz. In particular, he says, mass-loss rates for massive stars are not known well enough to assert a specific difference in carbon production between single and binary stars.

      Farmer acknowledges the uncertainty, but “the overall picture is sound,” he says. “The binaries are making more [carbon].” More

    • 150 Shares159 Views

      in Space & Astronomy

      Distant rocky planets may have exotic chemical makeups that don’t resemble Earth’s

      by

      If a real Captain Kirk ever blasts off for other stars in search of rocky planets like ours, he may find lots of strange new worlds whose innards actually bear no resemblance to Earth’s.

      A smattering of heavy elements sprinkled on 23 white dwarf stars suggests that most of the rocky planets that once orbited the stars had unusual chemical makeups, researchers report online November 2 in Nature Communications. The elements, presumably debris from busted-up worlds, provide a possible peek at the planets’ mantles, the region between their crust and core.

      “These planets could be just utterly alien to what we’re used to thinking of,” says geologist Keith Putirka of California State University, Fresno.  

      But deducing what a long-gone planet was made of from what it left behind is fraught with difficulties, cautions Caltech planetary scientist David Stevenson. Rocky worlds outside of the solar system may have exotic chemical compositions, he says. “It’s just that I don’t think this paper can be used to prove that.”

      Sign Up For the Latest from Science News

      Headlines and summaries of the latest Science News articles, delivered to your inbox

      Thank you for signing up!

      There was a problem signing you up.

      After a star like the sun expands into a red giant star, it ultimately blows off its atmosphere, leaving behind its small, dense core, which becomes a white dwarf. That star’s great gravity drags heavy chemical elements into its interior, so most white dwarfs have pristine surfaces of hydrogen and helium.

      But more than a quarter of these stars sport surfaces with heavier elements such as silicon and iron, presumably from planets that once circled the star and met their ends when it expanded into a red giant (SN: 8/15/11). The heavy elements on these white dwarfs haven’t yet had time to sink beneath the stellar surface.

      For that reason, Siyi Xu, an astronomer at the Gemini Observatory in Hilo, Hawaii, has long studied white dwarfs. Then she met Putirka. Because he’s a geologist, “he was like, ‘Oh! We can look at this problem from a new perspective,’” Xu says.

      Xu had been measuring the abundances of chemical elements littered on white dwarfs by studying the wavelengths of light, or spectra, given off by the stars. Putirka realized that those measurements could indicate what rocks and minerals had made up the destroyed planets’ mantles, which constitute the bulk of a small planet’s rock, because different rocks and minerals contain different chemical elements.

      By examining white dwarfs within 650 light-years of the sun, Putirka and Xu reached a startling conclusion about the ripped-apart rocky planets. Contrary to conventional wisdom, most of their planetary mantles didn’t resemble those of the sun’s rocky planets — Mercury, Venus, Earth and Mars, the researchers say.

      For example, some of the white dwarfs have lots of silicon. That suggests that their planets’ mantles had quartz — a mineral that in its pure form consists solely of silicon and oxygen. But there’s little, if any, quartz in Earth’s mantle. A planet with a quartz-rich mantle would probably differ greatly from Earth, Putirka says.

      Such exotic mineral compositions might affect, for example, volcanic eruptions, continental drift and the fraction of a planet’s surface that consists of oceans versus continents. And all those phenomena might affect the development of life.

      Stevenson, however, is skeptical of the new finding. When you measure the elemental composition of a “polluted white dwarf,” he says, “you do not know how to connect those numbers to what you started with.”

      That’s partly because the destruction of rocky worlds around sunlike stars is complicated, Stevenson says. The planets first get blasted by the red giant’s bright light. Then they may get engulfed by the star’s expanding atmosphere and may even crash into another planet.

      Each of these traumatic events could alter a planet’s elemental makeup, as well as possibly send some elements toward the white dwarf ahead of others. As a result, the planetary remains that end up on the star’s surface at one snapshot in time may not reflect the world’s starting composition.

      Xu agrees that astronomers don’t know precisely how the breakup plays out or which elements wind up falling onto the white dwarf. Future theoretical studies could provide insight into the matter, she says. 

      She also notes that astronomers have caught asteroids disintegrating around white dwarfs, which offer a small window into the actual breakup process. And future observations of these white dwarfs, she says, could help reveal any changes in elemental composition over time. More

    • 138 Shares169 Views

      in Space & Astronomy

      A stunning simulation re-creates how M87’s black hole launches plasma jets

      by

      From the maw of the supermassive black hole at the center of the galaxy M87, two enormous jets stream thousands of light-years into space. Scientists still don’t fully understand the physics behind the jets, which are made of a mix of electrically charged particles, or plasma (SN: 3/24/21). But they are “really, really amazing,” says astrophysicist Alejandro Cruz-Osorio of Goethe University Frankfurt. So he and colleagues created a computer simulation of M87’s black hole and the swirling gas that surrounds it in an accretion disk. The aim: Figure out how this black hole — already famous for posing for a picture in 2019 (SN: 4/10/19) — became such a jet-setter.

      Under the right conditions, that simulation produces jets that match observations of M87, the researchers report November 4 in Nature Astronomy. The black hole twists up spiraling magnetic fields that surround two high-energy beams of electrons and other charged particles. The results suggest that the black hole must be spinning rapidly, at more than half its maximum speed allowed by the laws of physics and possibly as much as 94 percent of its maximum possible speed.

      Getting the energies of the jets’ electrons right turned out to be crucial. When magnetic fields in the jets rearrange in a process known as magnetic reconnection (SN: 8/3/21), electrons get accelerated, resulting in more of them having very high energies. This effect was not included in earlier simulations, but it was key to getting the simulated jets to act like real-world counterparts. More

    • 138 Shares199 Views

      in Space & Astronomy

      Neutron star collisions probably make more gold than other cosmic smashups

      by

      The cosmic origins of elements heavier than iron are mysterious. One elemental birthplace came to light in 2017 when two neutron-rich dead stars collided and spewed out gold, platinum and other hefty elements (SN: 10/16/17). A few years later, a smashup of another neutron star and a black hole left scientists wondering which type of cosmic clash was the more prolific element foundry (SN: 6/29/21).

      Now, they have an answer. Collisions of two neutron stars probably take the cake, scientists report October 25 in Astrophysical Journal Letters.

      To create heavy elements after either type of collision, neutron star material must be flung into space, where a series of nuclear reactions called the r-process can transform the material (SN: 4/22/16).

      How much material escapes into space, if any, depends on various factors. For example, in collisions of a neutron star and black hole, the black hole has to be relatively small, or “there’s no hope at all,” says astrophysicist Hsin-Yu Chen of MIT. “It’s going to swallow the neutron star right away,” without ejecting anything.

      Questions remain about both types of collisions, spotted via the ripples in spacetime that they kick up. So Chen and colleagues considered a range of possibilities for the properties of neutron stars and black holes, such as the distributions of their masses and how fast they spin. The team then calculated the mass ejected by each type of collision under those varied conditions. In most scenarios, the neutron star–black hole mergers made a smaller quantity of heavy elements than the neutron star duos — in one case only about a hundredth the amount.

      Still, the ultimate element factory ranking remains up in the air. The scientists compared just these two types of collisions, not other possible sources of heavy elements such as exploding stars (SN: 7/7/21). More

    • 138 Shares199 Views

      in Space & Astronomy

      Pluto’s dark side reveals clues to its atmosphere and frost cycles

      by

      Pluto’s dark side has come into dim view, thanks to the light of the dwarf planet’s moon.

      When NASA’s New Horizons spacecraft flew past Pluto in 2015, almost all the images of the dwarf planet’s unexpectedly complex surface were of the side illuminated by the sun (SN: 7/15/15). Darkness shrouded the dwarf planet’s other hemisphere. Some of it, like the area near the south pole, hadn’t seen the sun for decades.

      Now, mission scientists have finally released a grainy view of the dwarf planet’s dark side. The researchers describe the process to take the photo and what it tells them about how Pluto’s nitrogen cycle affects its atmosphere October 20 in the Planetary Science Journal.

      Before New Horizons passed by Pluto, the team suspected the dwarf planet’s largest moon, Charon, might reflect enough light to illuminate the distant world’s surface. So the researchers had the spacecraft turn back toward the sun to take a parting peek at Pluto.

      New Horizons captured this view of the backlit dark side of Pluto as the spacecraft receded from the dwarf planet in 2015. Some light and dark splotches were illuminated by the dim light of Pluto’s moon Charon.NOIRLab, SwRI, JHUAPL, NASA

      At first, the images just showed a ring of sunlight filtering through Pluto’s hazy atmosphere (SN: 7/24/15). “It’s very hard to see anything in that glare,” says planetary scientist John Spencer of the Southwest Research Institute in Boulder, Colo. “It’s like trying to read a street sign when you’re driving toward the setting sun and you have a dirty windshield.”

      Spencer and colleagues took a few steps to make it possible to pull details of Pluto’s dark side out of the glare. First, the team had the spacecraft take 360 short snapshots of the backlit dwarf planet. Each was about 0.4 seconds long, to avoid overexposing the images. The team also took snapshots of the sun without Pluto in the frame so that the sun could be subtracted out after the fact.

      Tod Lauer of the National Optical Astronomy Observatory in Tucson, Ariz., tried to process the images when he got the data in 2016. At the time, the rest of the data from New Horizons was still fresh and took up most of his attention, so he didn’t have the time to tackle such a tricky project.

      But “it was something that just sat there and ate away at me,” Lauer says. He tried again in 2019. Because the spacecraft was moving as it took the images, each image was a little bit smeared or blurred. Lauer wrote a computer code to remove that blur from each individual frame. Then he added the reflected Charon light in each of those hundreds of images together to produce a single image.

      Sign Up For the Latest from Science News

      Headlines and summaries of the latest Science News articles, delivered to your inbox

      Thank you for signing up!

      There was a problem signing you up.

      “When Tod did that painstaking analysis, we finally saw something emerging in the dark there … giving us a little bit of a glimpse of what the dark pole of Pluto looks like,” Spencer says.

      That the team got anything at all is impressive, says planetary scientist Carly Howett, also of the Southwest Research Institute and who is on the New Horizons team but was not involved in this work. “This dataset is really, really hard to work with,” she says. “Kudos to this team. I wouldn’t have wanted to do this.”

      The image, Howett says, can help scientists understand how Pluto’s frigid nitrogen atmosphere varies with its decades-long seasons. Pluto’s atmosphere is controlled by how much nitrogen is in a gas phase in the air and how much is frozen on the surface. The more nitrogen ice that evaporates, the thicker the atmosphere becomes. If too much nitrogen freezes to the ground, the atmosphere could collapse altogether.

      In this image of Pluto’s sunlit side from NASA’s New Horizons spacecraft, different colors represent different kinds of ices. A faint glimpse of Pluto’s dark hemisphere in newly released mission images reveals some new details about how those ices behave.SwRI, JHUAPL, NASA

      When New Horizons was there, Pluto’s south pole looked darker than the north pole. That suggests there was not a lot of fresh nitrogen frost freezing out of the atmosphere there, even though it was nearing winter. “The previous summer ended decades ago, but Pluto cools off pretty slowly,” Spencer says. “Maybe it’s still so warm [that] the frost can’t condense there, and that keeps the atmosphere from collapsing.”

      There was a bright spot in the middle of the image, which could be a fresh ice deposit. That’s also not surprising, Howett says. The ices may still be moving from the north pole to the south pole as Pluto moves deeper into its wintertime.

      “We’ve thought this for a long time. It makes sense,” she says. “But it’s nice to see it happening.” More

    • 150 Shares179 Views

      in Space & Astronomy

      A rush to watch a supernova exposed its last gasp before exploding

      by

      A mad scramble to observe the moments after a star’s death is helping scientists understand how the star lived out its last year.

      Astronomers reported the exploding star just 18 hours after it flared up on March 31, 2020, in a galaxy about 60 million light-years away from Earth in the Virgo cluster. The supernova occurred in part of the sky already watched by NASA’s Transiting Exoplanet Survey Satellite, which images large portions of the sky every 30 minutes (SN: 1/8/19). And a team of scientists quickly realized that data would track precisely how the eruption brightened over time, making it ideal for further study. 

      To learn even more, the team leapt into action, viewing the supernova with a variety of telescopes in the hours and days that followed, even orchestrating a last-minute change of plans for the Hubble Space Telescope. That provided the supernova’s spectrum, an accounting of its light broken up by wavelength, at various moments after the blast.

      All that data revealed that in the last year of its life, the star had spewed some of its outer layers into space, researchers report October 26 in Monthly Notices of the Royal Astronomical Society. The amount of material ejected was about 0.23 times the mass of the sun, the team estimates. When the supernova went off, it launched a shock wave that plowed through that material shortly after the explosion, generating light picked up by the telescopes.

      As large stars get closer to death, they may start behaving erratically. Aging stars fuse heavier and heavier elements in their cores. For this star, the switch to fusing oxygen could have triggered that shedding in its last year, astrophysicist Samaporn Tinyanont of the University of California, Santa Cruz and colleagues suggest. “These stars have a roller coaster last few years of their life,” Tinyanont says.

      Scientists hope that understanding that roller coaster ride could help them recognize when other stars are about to blow. More

    • 150 Shares159 Views

      in Space & Astronomy

      What the Perseverance rover’s quiet landing reveals about meteor strikes on Mars

      by

      The lander was listening. On February 18, NASA’s InSight lander on Mars turned its attention to the landing site for another mission, Perseverance, hoping to detect its arrival on the planet.

      But InSight heard nothing.

      Tungsten blocks ejected by Perseverance during entry landed hard enough to create craters on the Martian surface. Collisions like these — whether from space missions or meteor strikes — send shock waves through the ground. Yet in the first experiment of its kind on another world, InSight failed to pick up any seismic waves from the blocks’ impacts, researchers report October 28 in Nature Communications.

      As a result, researchers think that less than 3 percent of the energy from the impacts made its way into the Martian surface. The intensity of impact-generated rumblings varies from planet to planet and is “really important for understanding how the ground will change from a big impact event,” says Ben Fernando, a geophysicist at the University of Oxford.

      Perseverance left behind several craters (one indicated with the arrow) after pieces of the mission disengaged as planned during entry, creating a rare opportunity to see how Mars absorbs energy from impacts. Univ. of Arizona, JPL-Caltech/NASA

      But getting these measurements is tricky. Scientists need sensitive instruments placed relatively near an impact site. Knowing when and where a meteor will strike is nearly impossible, especially on another world.

      Enter Perseverance: a hurtling space object set to hit Mars at an exact time and place (SN: 2/17/21). To help with its entry, Perseverance dropped about 78 kilograms of tungsten as the rover landed about 3,450 kilometers from InSight. The timing and weight of the drop provided a “once-in-a-mission opportunity” to study the immediate seismic effects of an impact from space, Fernando says.

      The team had no idea whether InSight would be able to detect the blocks’ impacts or not, but the quiet arrival speaks volumes. “It lets us put an upper limit on how much energy from the tungsten blocks turned into seismic energy,” Fernando says. “We’ve never been able to get that number for Mars before.”

      Sign Up For the Latest from Science News

      Headlines and summaries of the latest Science News articles, delivered to your inbox

      Thank you for signing up!

      There was a problem signing you up. More

    • 138 Shares119 Views

      in Space & Astronomy

      Astronomers may have spotted the first known exoplanet in another galaxy

      by

      Astronomers may have spotted the first known planet in another galaxy.

      The potential world, called M51-ULS-1b, orbits both a massive star and a dead star in the Whirlpool galaxy, about 28 million light-years from Earth. The object’s existence, if confirmed, suggests that there could be many other extragalactic exoplanets waiting to be discovered, astronomers report in a study to appear in Nature Astronomy.

      “We probably always assumed there would be planets” in other galaxies, says astrophysicist Rosanne Di Stefano of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. “But to actually find something, it’s a beautiful thing. It’s a humbling experience.”

      More than 4,800 planets have been discovered orbiting stars other than the sun, all of them inside the Milky Way. There’s no reason to think that other galaxies don’t also host planets. But the most popular exoplanet hunting techniques are difficult to do with such faraway stars, which blend together too much to observe them one by one.

      Sign Up For the Latest from Science News

      Headlines and summaries of the latest Science News articles, delivered to your inbox

      Thank you for signing up!

      There was a problem signing you up.

      In 2018, Di Stefano and astrophysicist Nia Imara of the University of California, Santa Cruz suggested searching for planets around extragalactic X-ray binaries.

      X-ray binaries usually consist of a massive star and the remains of a second massive star, which has collapsed into a neutron star or a black hole. The dead star steals material from the living star and heats it to such hot temperatures that it emits bright X-rays that stand out from the crowd of other stars.

      That X-ray region can be smaller than a giant planet, meaning if a planet crosses, or transits, in front of such a system from astronomers’ perspective on Earth, it could temporarily block all the X-rays, revealing the planet’s presence.

      Di Stefano and colleagues searched archived data from NASA’s Chandra X-ray telescope for signs of blinking X-ray sources (SN: 7/25/19). The team looked at a total of 2,624 possible transits in three galaxies: M51 (the Whirlpool galaxy), M101 (the Pinwheel galaxy) and M104 (the Sombrero galaxy).

      Only one turned up a clear planetlike signal. On September 20, 2012, an object had blocked all of the X-rays from the X-ray binary M51-ULS-1 for about three hours.

      “We said, ‘Wow. Could this be it?’” Di Stefano says.

      After ruling out gas clouds passing in front of the binary, fluctuations in the X-ray source itself or other explanations for the dip, Di Stefano and colleagues conclude that the object was most likely a Saturn-sized planet orbiting the X-ray binary hundreds of times the distance between Earth and the sun.

      This isn’t a comfortable environment for the planet. “You don’t want to be there,” Di Stefano notes. Despite its distance from the X-ray binary, the planet receives as much energy in X-rays and ultraviolet radiation as a hot Jupiter exoplanet, which orbits its star in just a few days, receives from an ordinary star (SN: 6/5/17).

      “The possibility that the team discovered the transit of an extragalactic planet is quite intriguing and would be a great discovery,” says astrophysicist Ignazio Pillitteri of the Italian National Institute for Astrophysics in Palermo. He would like to see the transit happen again to confirm it.

      Not everyone finds the result convincing. “I find the paper very speculative,” says astrophysicist Matthew Bailes of the Swinburne University of Technology in Melbourne, Australia. If the planet is real, finding it relied on a lot of coincidences: Its orbit needed to be perfectly aligned with the point of view from Earth, and it needed to just happen to be passing in front of the X-ray binary while Chandra was looking.

      Di Stefano counters that the fact that her team saw a signal within such a small number of observations suggests there are lots of extragalactic planets out there. “Maybe we were lucky,” she acknowledges. “But I think it’s very likely that we were not special. We looked and we found something because there was something to find.”

      Di Stefano doesn’t expect to see this particular planet again in her lifetime. It could take decades for it to pass in front of its host stars again. “The real test,” she says, “is finding more planets.” More