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      Record-breaking gravitational waves reveal that midsize black holes do exist

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      The biggest. The farthest. The most energetic. A new detection of gravitational waves from two colliding black holes has racked up multiple superlatives.
      What’s more, it also marks the first definitive sighting of an intermediate mass black hole, one with a mass between 100 and 100,000 times the sun’s mass. That midsize black hole was forged when the two progenitor black holes coalesced to form a larger one with about 142 solar masses. It significantly outweighs all black holes previously detected via gravitational waves, ripples that wrinkle spacetime in the aftermath of extreme events.
      “This is the big guy we’ve been waiting for, for the longest time,” says Emanuele Berti, a physicist at Johns Hopkins University who was not involved with the research. One of the behemoth’s two progenitors was itself so massive that scientists are pondering how to explain its existence.
      Detected on May 21, 2019, the gravitational waves originated from a source about 17 billion light-years from Earth, making this the most distant detection confirmed so far. It’s also the most energetic event yet seen, radiating about eight times the equivalent of the sun’s mass in energy, says astrophysicist Karan Jani of Vanderbilt University in Nashville, a member of the LIGO Scientific Collaboration. “I hope it deserves its own entry in the record book.”

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      The new event dethrones the previous record-holder, a collision that occurred about 9 billion light-years away that radiated about five solar masses worth of energy, and created a black hole of 80 solar masses (SN: 12/4/18).
      Researchers with LIGO, or the Advanced Laser Interferometer Gravitational-Wave Observatory, in the United States and Advanced Virgo in Italy reported the new detection September 2 in two papers in Physical Review Letters and the Astrophysical Journal Letters.
      While scientists know of black holes with tens of solar masses and others with millions or billions of solar masses, the intermediate echelon has remained elusive. Previous purported sightings of intermediate mass black holes have been questioned (SN:1/22/16).
      But, for the new event, “there’s no doubt,” says astrophysicist Cole Miller of University of Maryland at College Park, who was not involved with the study. “This demonstrates that there is now at least one intermediate mass black hole in the universe.”
      The black hole’s two progenitors were themselves heftier than any seen colliding before — at about 85 and 66 times the mass of the sun. That has scientists puzzling over how this smashup came to be.

      Normally, physicists expect that the black holes involved in these mergers would each have formed in the collapse of a dying star. But in the new event, the larger of the pair is so big that it couldn’t have formed that way. The known processes that go on within a star’s core mean that stars that are the right mass to form such a big black hole would blow themselves apart completely, rather than leaving behind a corpse.
      Instead, it might be that one or both of the colliding black holes formed from an earlier round of black hole mergers, within a crowded cluster of stars and black holes (SN: 1/30/17). That would make for a family tree that began with black holes lightweight enough to form from collapsing stars.
      But there’s a problem with the multiple-merger explanation. Each time black holes merge, that coalescence provides a kick to their velocity, which would normally launch the resulting black hole out of the cluster, preventing further mergers.
      However, mergers as massive as the new event seem to be very rare, given that LIGO and Virgo have detected only one. That means, Miller says, “my gosh, you’re allowed to invoke a tooth fairy,” a relatively unlikely process. Perhaps, he says, the kick might sometimes be small enough that the black holes could stay within their cluster and merge again.
      The May 21 gravitational wave event had previously been publicly reported as an unconfirmed candidate, to allow astronomers to look for flashes of light in the sky that might have resulted from the collision. Some researchers had suggested that the waves might have been associated with a flare of light from the center of a distant galaxy (SN: 6/25/20). But that galaxy is significantly closer than the distance now pinpointed in the new papers, at about 8 billion light-years from Earth rather than 17 billion, making the explanation less plausible.
      The longer LIGO and Virgo observe the heavens, the more the bounty of unusual events can be expected to grow, Miller says. “We are going to have a set of ‘gosh, didn’t expect that’ type of events, which are thrilling to think about and extremely informative about the universe.” More

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      Earth’s building blocks may have had far more water than previously thought

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      Earth’s deep stores of water may have been locally sourced rather than trucked in from far-flung regions of the solar system.
      A new analysis of meteorites from the inner solar system — home to the four rocky planets — suggests that Earth’s building blocks delivered enough water to account for all the H2O buried within the planet. What’s more, the water produced by the local primordial building material likely shares a close chemical kinship with Earth’s deep-water reserves, thus strengthening the connection, researchers report in the Aug. 28 Science.
      Earth is thought to have been born in an interplanetary desert, too close to the sun for water ice to survive. Many researchers suspect that ocean water got delivered toward the end of Earth’s formation by ice-laden asteroids that wandered in from cooler, more distant regions of the solar system (SN: 5/6/15). But the ocean isn’t the planet’s largest water reservoir. Researchers estimate that Earth’s interior holds several times as much water as is found at the surface.
      To test whether or not the material that formed Earth could have delivered this deep water, cosmochemist Laurette Piani of the University of Lorraine in Vandœuvre-lès-Nancy, France, and colleagues analyzed meteorites known as enstatite chondrites. Thanks to many chemical similarities with Earth rocks, these relatively rare meteorites are widely thought to be good analogs of the dust and space rocks from the inner solar system that formed Earth’s building blocks, Piani says.

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      She and her team measured the abundance of hydrogen in these meteorites — a proxy for how much H2O they could produce — and calculated that local interplanetary debris had the potential to deliver at least three times as much water as is found in all the oceans. The meteorites don’t contain water, Piani says. Rather, they house enough of the raw ingredients to create water when heated.
      In the meteorites, the team also found a close match to the type of water found in Earth’s mantle. A smattering of all water molecules on Earth contain a heavy variant of hydrogen known as deuterium. The ratio of deuterium to hydrogen in the enstatite chondrites lies within the range measured in Earth’s deep water. That similarity, the team argues, makes a strong case for local building blocks being the source of much of the planet’s water.
      “This work is something I wanted to do myself or had been waiting for someone to do,” says Lydia Hallis, a planetary scientist at the University of Glasgow in Scotland. In 2015, she led a team that measured the deuterium abundance in lava plumes that tap deep into Earth’s mantle (SN: 11/12/15). “I’m really happy that [the new data] sits within the region where our previous data from deep mantle samples is sitting.”
      Hallis and others stress that these new measurements are difficult. Once the meteorites hit the ground, they quickly absorb hydrogen from Earth’s environment. “They did a really good job of picking the right meteorites and making the right measurements,” she says. “This is pretty convincing that this hydrogen that’s measured is from the enstatite chondrites rather than from terrestrial contamination.”
      The enstatite chondrites could have also contributed a lot of water to the oceans as well — but they are not the full story. The deuterium-hydrogen ratio in ocean water, which is a bit higher than that of mantle water, is better matched to the ratio found in icy asteroids from the outer solar system. “We still need a bit of water coming from the outer solar system,” Piani says. So, while local materials may have delivered the bulk of Earth’s water, the oceans were likely topped off a bit later by collisions with remote space rocks. More

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      Check out the first-ever map of the solar corona’s magnetic field

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      The sun’s wispy upper atmosphere, called the corona, is an ever-changing jungle of sizzling plasma. But mapping the strength of the magnetic fields that largely control that behavior has proved elusive. The fields are weak and the brightness of the sun outshines its corona.
      Now though, observations taken using a specialized instrument called a coronagraph to block out the sun’s bright disk have allowed solar physicists to measure the speed and intensity of waves rippling through coronal plasma (SN: 3/19/09). “This is the first time we’ve mapped the coronal magnetic field on a large scale,” says Steven Tomczyk, a solar physicist at the High Altitude Observatory in Boulder, Colo., who designed the coronagraph.
      In 2017, Tomczyk had been part of a team that took advantage of a total solar eclipse crisscrossing North America to take measurements of the corona’s magnetic field (SN: 8/16/17). He trekked to a mountaintop in Wyoming with a special camera to snap polarized pictures of the corona just as the moon blocked the sun.  (I was there with them, reporting on the team’s efforts to help explain why the corona is so much hotter than the sun’s surface (SN: 8/21/17).) The team observed a tiny slice of the corona to test whether a particular wavelength of light could carry signatures of the corona’s magnetic field. It can (SN: 8/21/18).
      But it’s the observations from the coronagraph, made in 2016, that allowed researchers to look at the whole corona all at once. Theorists had shown decades ago that coronal waves’ velocities can be used to infer the strength of the magnetic field. Such waves might also help carry heat from the sun’s surface into the corona (SN: 11/14/19). But no one had measured them across the whole corona before.

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      The corona’s magnetic field strength is mostly between 1 and 4 gauss, a few times the strength of the Earth’s magnetic field at the planet’s surface, the researchers report in the Aug. 7 Science.
      Making a map is a big step, the team says. But what solar physicists would really like to do is track the corona’s magnetic field continuously, at least once a day.
      “The solar magnetic field is evolving all the time,” says solar physicist Zihao Yang of Peking University in Beijing. Sometimes the sun releases magnetic energy explosively, sending bursts of plasma can shooting out into space (SN: 3/7/19). Those ejections can wreak havoc on satellites or power grids when they strike Earth. Continuously monitoring coronal magnetism can help predict those outbursts. “Our work demonstrated that we can use this technique to map the global distribution of coronal magnetic field, but we only showed one map from a single dataset,” Yang says.
      Measuring the strength of the corona’s magnetic field is “a really big deal,” says solar physicist Jenna Samra of the Smithsonian Astrophysical Observatory in Cambridge, Mass. “Making global maps of the coronal magnetic field strength … is what’s going to allow us to eventually get better predictions of space weather events,” she says. “This is a really nice step in that direction.”
      Tomczyk and colleagues are working on an upgraded version of the coronagraph, called COSMO, for Coronal Solar Magnetism Observatory, that would use the same technique repeatedly with the ultimate goal of predicting the sun’s behavior.
      “It’s a milestone to do it,” Tomczyk says. “The goal is to do it regularly, do it all the time.” More

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      In a first, astronomers spotted a space rock turning into a comet

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      Like the mythical half-human, half-horse creatures, centaurs in the solar system are hybrids between asteroids and comets. Now, astronomers have caught one morphing from one type of space rock to the other, potentially giving scientists an unprecedented chance to watch a comet form in real time in the decades to come.
      “We have an opportunity here to see the birth of a comet as it starts to become active,” says planetary scientist Kat Volk of the University of Arizona in Tucson.
      The object, called P/2019 LD2, was discovered by the ATLAS telescope in Hawaii in May. Its orbit suggests that it’s a centaur, a class of rocky and icy objects with unstable orbits. Because of that mixed composition and potential to move around the solar system, astronomers have long suspected that centaurs are a missing link between small icy bodies in the Kuiper Belt beyond Neptune and comets that regularly visit the inner solar system (SN: 11/19/94).
      These “short-period” comets, which are thought to originate from icy objects in the Kuiper Belt, orbit the sun once a decade or so, and make repeat appearances in Earth’s skies. (Long-period comets, like Halley’s Comet, which visits the inner solar system once a century, probably originate even farther from the sun, in the Oort cloud (SN: 10/25/13).)

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      All previously found short-period comets were spotted only after they had transitioned into comets (SN: 8/6/14). But LD2 just came in from the Kuiper Belt recently and will become a comet in as little as 43 years, Volk and colleagues report August 10 at arXiv.org.
      “It’s weird to think that this object should be becoming a comet when I’m retiring,” Volk says.
      In 2019, she and colleagues showed that there’s a region of space just beyond Jupiter that they call the “Gateway”.  In this area, small planetary objects hang out while warming up and transitioning from outer solar system ice balls to inner solar system comets with their long tails. It’s like a comet incubator, says planetary scientist Gal Sarid of the SETI Institute, who is based in Rockville, Md.
      After hearing about LD2, Volk, Sarid and their colleagues simulated thousands of possible trajectories to see where the object had been and where it is going. LD2’s orbit probably took it near Saturn around 1850, and it entered its current orbit past Jupiter after a close encounter with the gas giant in 2017, the team found. The object will leave its present orbit and move in toward the sun in 2063, where heat from the sun will probably sublimate LD2’s volatile elements, giving it a bright cometary tail, the researchers say.
      “This will be the first ever comet that we know its history, because we’ve seen it before being a comet,” Sarid says.
      The fact that LD2 is fairly new to the inner reaches of the solar system suggests that it’s made of relatively pristine material that has been in the back of the solar system’s freezer for billions of years, unaltered by heat from the sun. That would make it a time capsule of the early solar system. Studying its composition could help planetary scientists learn what the first planets were made of.
      The orbital analysis looks “very reasonable,” says Henry Hsieh, a planetary astronomer with the Planetary Science Institute who is based in Honolulu and was not involved in the study. But studying just one transition object is not enough to open the solar system time capsule.
      “What we really need to do is study many of these,” he says. “Study this one first, and then study more of them, and figure out whether this object is an outlier or whether we see a consistent picture.” Future sky surveys, like the ones planned using the future Vera Rubin Observatory (SN: 1/10/20), should discover more balls of ice shifting into comets.
      Sarid and colleagues think LD2 could be a good target for a spacecraft to visit. NASA has considered sending spacecraft to centaurs, although no missions have been selected for development yet. But considering that LD2 will become a comet in just a few decades, scientists don’t have much time to plan, build and launch a mission to visit it. “The windows are closing,” Sarid says. “We really need to be doing this now.” More

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      Hubble watched a lunar eclipse to see Earth from an alien’s perspective

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      To practice searching for extraterrestrial life, researchers have run a dress rehearsal with the one world they know to be habitable: Earth.
      While Earth was between the sun and moon for a lunar eclipse in January 2019, the Hubble Space Telescope observed how chemicals in Earth’s atmosphere blocked certain wavelengths of sunlight from reaching the moon. That observing setup mimicked the way astronomers plan to probe the atmospheres of Earthlike exoplanets as they pass in front of their stars, filtering out some starlight.
      “We basically pretend we’re alien observers looking at our planet,” says Giada Arney, a planetary scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md.
      Using Hubble, the researchers focused on spotting the effects of atmospheric ozone. Because ozone is both a chemical by-product of oxygen produced in photosynthesis and a shield that protects life from the sun’s harmful ultraviolet rays, astronomers think atmospheric ozone could be a key indicator that a distant world is habitable. During the lunar eclipse, Hubble examined sunlight that had passed through Earth’s atmosphere and reflected off of the moon for signatures of ozone.

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      “It’s safer for Hubble to observe sunlight reflected off the moon” than to look directly at the backlit Earth, explains Allison Youngblood, an astronomer at the University of Colorado Boulder. The telescope’s instruments are so sensitive and Earth is so bright that “even the nightside would fry Hubble’s detectors.” 
      Those observations revealed prominent dips in particular wavelengths of ultraviolet sunlight that had been absorbed by the ozone, Youngblood, Arney and colleagues report online August 6 in the Astronomical Journal.
      The data help confirm that chemicals in the Earth’s atmosphere filter light as expected, based on researchers’ understanding of atmospheric chemistry. That finding gives astronomers more confidence that they will be able to recognize potentially habitable exoplanets. More

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      Scientists can’t agree on how clumpy the universe is

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      The universe is surprisingly smooth.
      A new measurement reveals that the universe is less clumpy than predicted, physicists report in a series of papers posted July 30 at arXiv.org. The discrepancy could hint at something amiss with scientists’ understanding of the cosmos.
      To pin down the cosmic clumpiness, researchers studied the orientation of 21 million galaxies with the Kilo-Degree Survey at the Paranal Observatory in Chile. As light from those galaxies streams through the universe, its trajectory is bent by massive objects, a phenomenon called gravitational lensing. This lensing causes the elongated shapes of galaxies to appear slightly aligned, rather than oriented randomly.
      When combined with additional data from other sky surveys, that alignment quantifies how much the matter in the universe is clumped together. The researchers found that the universe is about 10 percent more homogenous, or smoother, than predicted based on light released just after the Big Bang, the cosmic microwave background. Previous results had hinted at the discrepancy, but the new measurement strengthens the case that the disagreement is not a fluke (SN: 7/30/19).
      If the measurement is correct, the mismatch could hint at a hole in the standard model of cosmology, the theory that describes how the universe has changed over time. When combined with a similar puzzle over how fast the universe is expanding (SN: 7/15/20), physicists are beginning to suspect that the universe is putting them­­­­­ on notice.
      “It’s a bit of a riddle,” says cosmologist Hendrik Hildebrandt of Ruhr-Universität Bochum in Germany, a coauthor of the studies. “Is [the universe] just telling us ‘You’re stupid and you didn’t do your measurement right,’ or … ‘Hey, I’m more complicated than you thought’?” More

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      Jupiter’s moons could keep each other warm by raising tidal waves

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      It takes a certain amount of heat to keep an ocean wet. For Jupiter’s largest moons, a new analysis suggests a surprising source for some of that heat: each other.
      Three of the gas giant’s four largest moons, Ganymede, Callisto and Europa, are thought to harbor oceans of liquid water beneath their icy shells (SN: 5/14/18). The fourth, the volcanic moon Io, may contain an inner magma ocean (SN: 8/6/14).
      One of the primary explanations for how these small worlds stay warm enough to harbor liquid water or magma is gravitational kneading, or tidal forces, from their giant planetary host. Jupiter’s huge mass stretches and squishes the moons as they orbit, which creates friction and generates heat.
      But no studies had seriously considered how much heat the moons could get from gravitationally squishing each other.

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      “Because [the moons are] so much smaller than Jupiter, you’d think basically the tides raised by Io on Europa are just so small that they’re not even worth thinking about,” says planetary scientist Hamish Hay of NASA’s Jet Propulsion Laboratory in Pasadena, Calif.
      Together with planetary scientists Antony Trinh and Isamu Matsuyama, both of the University of Arizona in Tucson, Hay calculated the size of the tides that Jupiter’s moons would raise on each other’s oceans. The team reported the results July 19 in Geophysical Research Letters.
      The researchers found that the significance of the tides depends on how thick the ocean is. But with the right-sized ocean, neighboring moons could push and pull tidal waves on each other at the right frequency to build resonance. It’s a similar effect to pumping your legs on a swing, or synchronized footfalls making a bridge wobble, Hay says.
      “When you get into one of these resonances, those tidal waves start to get bigger,” he says. Those waves would then rush around the moon’s interior and generate heat through friction, the researchers calculated. If the conditions are right, heat from the gushing tidal waves could exceed heat from Jupiter.
      The effect was biggest between Io and Europa, the team found.
      “Basically everyone neglected these moon-moon effects,” says planetary scientist Cynthia Phillips of NASA’s Jet Propulsion Laboratory, who was not involved in the new work. “I was just astonished … at the amount of heating” that the moons may give each other, she says.
      The extra infusion of energy into Europa’s ocean could be good news for the possibility of alien life. Europa’s subsurface ocean is thought to be one of the best places in the solar system to look for extraterrestrial life (SN: 4/8/20). But anything living needs fuel, and the sun is too far away to be useful, Phillips says.
      “You have to find other sources of energy,” she says. “Any kind of frictional or heating energy is really exciting for life.” More