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.”

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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

A new map of the entire sky, as seen in X-rays, looks deeper into space than any other of its kind. The map, released June 19, is based on data from the first full scan of the sky made by the eROSITA X-ray telescope onboard the Russian-German SRG spacecraft, which launched in July 2019. The […] More

Albert Einstein’s mind reinvented space and time, foretelling a universe so bizarre and grand that it has challenged the limits of human imagination. An idea born in a Swiss patent office that evolved into a mature theory in Berlin set forth a radical new picture of the cosmos, rooted in a new, deeper understanding of gravity.
Out was Newton’s idea, which had reigned for nearly two centuries, of masses that appeared to tug on one another. Instead, Einstein presented space and time as a unified fabric distorted by mass and energy. Objects warp the fabric of spacetime like a weight resting on a trampoline, and the fabric’s curvature guides their movements. With this insight, gravity was explained.
Einstein presented his general theory of relativity at the end of 1915 in a series of lectures in Berlin. But it wasn’t until a solar eclipse in 1919 that everyone took notice. His theory predicted that a massive object — say, the sun — could distort spacetime nearby enough to bend light from its straight-line course. Distant stars would thus appear not exactly where expected. Photographs taken during the eclipse verified that the position shift matched Einstein’s prediction. “Lights all askew in the heavens; men of science more or less agog,” declared a New York Times headline.
Even a decade later, a story in Science News Letter, the predecessor of Science News, wrote of “Riots to understand Einstein theory” (SN: 2/1/30, p. 79). Apparently extra police had to be called in to control a crowd of 4,500 who “broke down iron gates and mauled each other” at the American Museum of Natural History in New York City to hear an explanation of general relativity.

By 1931, physicist Albert A. Michelson, the first American to win a Nobel Prize in the sciences, called the theory “a revolution in scientific thought unprecedented in the history of science.”
But for all the powers of divination we credit to Einstein today, he was a reluctant soothsayer. We now know that general relativity offered much more than Einstein was willing or able to see. “It was a profoundly different way of looking at the universe,” says astrophysicist David Spergel of the Simons Foundation’s Flatiron Institute in New York City, “and it had some wild implications that Einstein himself didn’t want to accept.” What’s more, says Spergel (a member of the Honorary Board of the Society for Science, publisher of Science News), “the wildest aspects of general relativity have all turned out to be true.”
What had been masquerading as a quiet, static, finite place is instead a dynamic, ever-expanding arena filled with its own riot of space-bending beasts. Galaxies congregate in superclusters on scales vastly greater than anything experts had considered before the 20th century. Within those galaxies reside not only stars and planets, but also a zoo of exotic objects illustrating general relativity’s propensity for weirdness, including neutron stars, which pack a fat star’s worth of mass into the size of a city, and black holes, which pervert spacetime so strongly that no light can escape. And when these behemoths collide, they shake spacetime, blasting out ginormous amounts of energy. Our cosmos is violent, evolving and filled with science fiction–like possibilities that actually come straight out of general relativity.
“General relativity opened up a huge stage of stuff for us to look at and try out and play with,” says astrophysicist Saul Perlmutter of the University of California, Berkeley. He points to the idea that the universe changes dramatically over its lifetime — “the idea of a lifetime of a universe at all is a bizarre concept” — and the idea that the cosmos is expanding, plus the thought that it could collapse and come to an end, and even that there might be other universes. “You get to realize that the world could be much more interesting even than we already ever imagined it could possibly be.”

General relativity has become the foundation for today’s understanding of the cosmos. But the current picture is far from complete. Plenty of questions remain about mysterious matter and forces, about the beginnings and the end of the universe, about how the science of the big meshes with quantum mechanics, the science of the very small. Some astronomers believe a promising route to answering some of those unknowns is another of general relativity’s initially underappreciated features — the power of bent light to magnify features of the cosmos.
Today’s scientists continue to poke and prod at general relativity to find clues to what they might be missing. General relativity is now being tested to a level of precision previously impossible, says astrophysicist Priyamvada Natarajan of Yale ​University. “General relativity expanded our cosmic view, then gave us sharper focus on the cosmos, and then turned the tables on it and said, ‘now we can test it much more strongly.’ ” It’s this testing that will perhaps uncover problems with the theory that might point the way to a fuller picture.
And so, more than a century after general relativity debuted, there’s plenty left to foretell. The universe may turn out to be even wilder yet.
Ravenous beasts
Just over a century after Einstein unveiled general relativity, scientists obtained visual confirmation of one of its most impressive beasts. In 2019, a global network of telescopes revealed a mass warping spacetime with such fervor that nothing, not even light, could escape its snare. The Event Horizon Telescope released the first image of a black hole, at the center of galaxy M87 (SN: 4/27/19, p. 6).
In 2019, the Event Horizon Telescope Collaboration released this first-ever image of a black hole, at the heart of galaxy M87. The image shows the shadow of the monster surrounded by a bright disk of gas.Event Horizon Telescope Collaboration
“The power of an image is strong,” says Kazunori Akiyama, an astrophysicist at the MIT Haystack Observatory in Westford, Mass., who led one of the teams that created the image. “I somewhat expected that we might see something exotic,” Akiyama says. But after looking at the first image, “Oh my God,” he recalls thinking, “it’s just perfectly matching with our expectation of general relativity.”
For a long time, black holes were mere mathematical curiosities. Evidence that they actually reside out in space didn’t start coming in until the second half of the 20th century. It’s a common story in the annals of physics. An oddity in some theorist’s equation points to a previously unknown phenomenon, which kicks off a search for evidence. Once the data are attainable, and if physicists get a little lucky, the search gives way to discovery.
In the case of black holes, German physicist Karl Schwarzschild came up with a solution to Einstein’s equations near a single spherical mass, such as a planet or a star, in 1916, shortly after Einstein proposed general relativity. Schwarzschild’s math revealed how the curvature of spacetime would differ around stars of the same mass but increasingly smaller sizes — in other words, stars that were more and more compact. Out of the math came a limit to how small a mass could be squeezed. Then in the 1930s, J. Robert Oppenheimer and Hartland Snyder described what would happen if a massive star collapsing under the weight of its own gravity shrank past that critical size — today known as the “Schwarzschild radius” — reaching a point from which its light could never reach us. Still, Einstein — and most others — doubted that what we now call black holes were plausible in reality.
The term “black hole” first appeared in print in Science News Letter. It was in a 1964 story by Ann Ewing, who was covering a meeting in Cleveland of the American Association for the Advancement of Science (SN: 1/18/64, p. 39). That’s also about the time that hints in favor of the reality of black holes started coming in.
Just a few months later, Ewing reported the discovery of quasars — describing them in Science News Letter as “the most distant, brightest, most violent, heaviest and most puzzling sources of light and radio waves” (SN: 8/15/64, p. 106). Though not linked to black holes at the time, quasars hinted at some cosmic powerhouses needed to provide such energy. The use of X-ray astronomy in the 1960s revealed new features of the cosmos, including bright beacons that could come from a black hole scarfing down a companion star. And the motions of stars and gas clouds near the centers of galaxies pointed to something exceedingly dense lurking within.  
Quasars (one illustrated) are so bright that they can outshine their home galaxies. Though baffling when first discovered, these outbursts are powered by massive, feeding black holes.Mark Garlick/Science Source
Black holes stand out among other cosmic beasts for how extreme they are. The largest are many billion times the mass of the sun, and when they rip a star apart, they can spit out particles with 200 trillion electron volts of energy. That’s some 30 times the energy of the protons that race around the world’s largest and most powerful particle accelerator, the Large Hadron Collider.
As evidence built into the 1990s and up to today, scientists realized these great beasts not only exist, but also help shape the cosmos. “These objects that general relativity predicted, that were mathematical curiosities, became real, then they were marginal. Now they’ve become central,” says Natarajan.
We now know supermassive black holes reside at the centers of most if not all galaxies, where they generate outflows of energy that affect how and where stars form. “At the center of the galaxy, they define everything,” she says.
Though visual confirmation is recent, it feels as though black holes have long been familiar. They are a go-to metaphor for any unknowable space, any deep abyss, any endeavor that consumes all our efforts while giving little in return.
Real black holes, of course, have given plenty back: answers about our cosmos plus new questions to ponder, wonder and entertainment for space fanatics, a lost album from Weezer, numerous episodes of Doctor Who, the Hollywood blockbuster Interstellar.
For physicist Nicolas Yunes of the University of Illinois at Urbana-Champaign, black holes and other cosmic behemoths continue to amaze. “Just thinking about the dimensions of these objects, how large they are, how heavy they are, how dense they are,” he says, “it’s really breathtaking.”
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In 2019, scientists gave us the first real picture of the supermassive black hole at the center of galaxy M87. How? We explain.
Spacetime waves
When general relativity’s behemoths collide, they disrupt the cosmic fabric. Ripples in spacetime called gravitational waves emanate outward, a calling card of a tumultuous and most energetic tango.
Einstein’s math predicted such waves could be created, not only by gigantic collisions but also by explosions and other accelerating bodies. But for a long time, spotting any kind of spacetime ripple was a dream beyond measure. Only the most dramatic cosmic doings would create signals that were large enough for direct detection. Einstein, who called the waves gravitationswellen, was unaware that any such big events existed in the cosmos.
Gravitational waves ripple away from two black holes that orbit each other before merging (shown in this simulation). The merging black holes created a new black hole that’s much larger than those found in previous collisions.Deborah Ferguson, Karan Jani, Deirdre Shoemaker and Pablo Laguna/Georgia Tech, Maya Collaboration
Beginning in the 1950s, when others were still arguing whether gravitational waves existed in reality, physicist Joseph Weber sunk his career into trying to detect them. After a decade-plus effort, he claimed detection in 1969, identifying an apparent signal perhaps from a supernova or from a newly discovered type of rapidly spinning star called a pulsar. In the few years after reporting the initial find, Science News published more than a dozen stories on what it began calling the “Weber problem” (SN: 6/21/69, p. 593). Study after study could not confirm the results. What’s more, no sources of the waves could be found. A 1973 headline read, “The deepening doubt about Weber’s waves” (SN: 5/26/73, p. 338).
Weber stuck by his claim until his death in 2000, but his waves were never verified. Nonetheless, scientists increasingly believed gravitational waves would be found. In 1974, radio astronomers Russell Hulse and Joseph Taylor spotted a neutron star orbiting a dense companion. Over the following years, the neutron star and its companion appeared to be getting closer together by the distance that would be expected if they were losing energy to gravitational waves. Scientists soon spoke not of the Weber problem, but of what equipment could possibly pick up the waves. “Now, although they have not yet seen, physicists believe,” Dietrick E. Thomsen wrote in Science News in 1984 (SN: 8/4/84, p. 76).
It was a different detection strategy, decades in the making, that would provide the needed sensitivity. The Advanced Laser Interferometry Gravitational-wave Observatory, or LIGO, which reported the first confirmed gravitational waves in 2016, relies on two detectors, one in Hanford, Wash., and one in Livingston, La. Each detector splits the beam of a powerful laser in two, with each beam traveling down one of the detector’s two arms. In the absence of gravitational waves, the two beams recombine and cancel each other out. But if gravitational waves stretch one arm of the detector while squeezing the other, the laser light no longer matches up.

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The machines are an incredible feat of engineering. Even spacetime ripples detected from colliding black holes might stretch an arm of the LIGO detector by as little as one ten-thousandth of the width of a proton.
When the first detection, from two colliding black holes, was announced, the discovery was heralded as the beginning of a new era in astronomy. It was Science News’ story of the year in 2016, and such a big hit that the pioneers of the LIGO detector won the Nobel Prize in physics the following year.
Scientists with LIGO and another gravitational wave detector, Virgo, based in Italy, have by now logged dozens more detections (SN: 1/30/21, p. 30). Most of the waves have emanated from mergers of black holes, though a few events have featured neutron stars. Smashups so far have revealed the previously unknown birthplaces of some heavy elements and pointed to a bright jet of charged subatomic particles that could offer clues to mysterious flashes of high-energy light known as gamma-ray bursts. The waves also have revealed that midsize black holes, between 100 and 100,000 times the sun’s mass, do in fact exist — along with reconfirming that Einstein was right, at least so far.
Researchers at two gravitational wave observatories, LIGO in the United States and Virgo in Italy (shown), have reported dozens of detections of black hole smashups, as well as neutron star mergers, in the last five years.The Virgo Collaboration
Just five years in, some scientists are already eager for something even more exotic. In a Science News article about detecting black holes orbiting wormholes via gravitational waves, physicist Vítor Cardoso of Instituto Superior Técnico in Lisbon, Portugal, suggested a coming shift to more unusual phenomena: “We need to look for strange but exciting signals,” he said (SN: 8/29/20, p. 12).
Gravitational wave astronomy is truly only at its beginnings. Improved sensitivity at existing Earth-based detectors will turn up the volume on gravitational waves, allowing detections from less energetic and more distant sources. Future detectors, including the space-based LISA, planned for launch in the 2030s, will get around the troublesome noise that interferes when Earth’s surface shakes.
“Perhaps the most exciting thing would be to observe a small black hole falling into a big black hole, an extreme mass ratio inspiraling,” Yunes says. In such an event, the small black hole would zoom back and forth, back and forth, swirling in different directions as it followed wildly eccentric orbits, perhaps for years. That could offer the ultimate test of Einstein’s equations, revealing whether we truly understand how spacetime is warped in the extreme. More

The Number of the HeavensTom SiegfriedHarvard Univ., $29.95 There is no bigger question than whether the universe is all there is. Scientists are juggling several ideas for what a multiverse, if one exists, might be like. Our universe could be one bubble in a vast cosmic fizz. Or one of many 3-D domains stacked, like […] More

First of two parts

In mystery stories, the chief suspect almost always gets exonerated before the end of the book. Typically because a key piece of evidence turned out to be wrong.

In science, key evidence is supposed to be right. But sometimes it’s not. In the mystery of the invisible “dark matter” in space, evidence implicating one chief suspect has now been directly debunked. WIMPs, tiny particles widely regarded as prime dark matter candidates, have failed to appear in an experiment designed specifically to test the lone previous study claiming to detect them.

For decades, physicists have realized that most of the universe’s matter is nothing like earthly matter, which is made mostly from protons and neutrons. Gravitational influences on visible matter (stars and galaxies) indicate that some dark stuff of unknown identity pervades the cosmos. Ordinary matter accounts for less than 20 percent of the cosmic matter abundance.

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For unrelated reasons, theorists have also long suggested that nature possesses mysterious types of tiny particles predicted by a theoretical mathematical framework known as supersymmetry, or SUSY for short. Those particles would be massive by subatomic standards but would interact only weakly with other matter, and so are known as Weakly Interacting Massive particles, hence WIMPs.

Of the many possible species of WIMPs, one (presumably the lightest one) should have the properties necessary to explain the dark matter messing with the motion of stars and galaxies (SN: 12/27/12). Way back in the last century, searches began for WIMPs in an effort to demonstrate their existence and identify which species made up the dark matter.

In1998, one research team announced apparent success. An experiment called DAMA (for DArk MAtter, get it?), consisting of a particle detector buried under the Italian Alps, seemingly did detect particles with properties matching some physicists’ expectations for a dark matter signal.

It was a tricky experiment to perform, relying on the premise that space is full of swarms of WIMPs. A detector containing chunks of sodium iodide should give off a flash of light when hit by a WIMP. But other particles from natural radioactive substances would also produce flashes of light even if WIMPs are a myth.

So the experimenters adopted a clever suggestion proposed earlier by physicists Katherine Freese, David Spergel and Andrzej Drukier, known formally as an annual modulation test. But let’s just call it the June-December approach.

As the Earth orbits the sun, the sun also moves, traveling around the Milky Way galaxy, carried by a spiral arm in the direction of the constellation Cygnus. If the galaxy really is full of WIMPs, the sun should be constantly plowing through them, generating a “WIMP wind.” (It’s like the wind you feel if you stick your head out of the window of a moving car.) In June, the Earth’s orbit moves it in the same direction as the sun’s motion around the galaxy — into the wind. But in December, the Earth moves the opposite direction, away from the wind. So more WIMPs should be striking the Earth in June than in December. It’s just like the way your car windshield smashes into more raindrops when driving forward than when going in reverse.

As the sun moves through space, it should collide with dark matter particles called WIMPs, if they exist. When the Earth’s revolution carries it in the same direction as the sun, in summer, the resulting “WIMP wind” should appear stronger, with more WIMP collisions detected in June than in December.GEOATLAS/GRAPHI-OGRE, ADAPTED BY T. DUBÉ

At an astrophysics conference in Paris in December 1998, Pierluigi Belli of the DAMA team reported a clear signal (or at least a strong hint) that more particles arrived in June than December. (More precisely, the results showed an annual modulation in frequency of light flashes, peaking around June with a minimum in December.) The DAMA data indicated a WIMP weighing in at 59 billion electron volts, roughly 60 times the mass of a proton.

But some experts had concerns about the DAMA team’s data analysis. And other searches for WIMPs, with different detectors and strategies, should have found WIMPs if DAMA was right — but didn’t. Still, DAMA persisted. An advanced version of the experiment, DAMA/LIBRA, continued to find the June-December disparity.

Perhaps DAMA was more sensitive to WIMPs than other experiments. After all, the other searches did not duplicate DAMA’s methods. Some used substances other than sodium iodide as a detecting material, or watched for slight temperature increases as a sign of a WIMP collision rather than flashes of light.

For that matter, WIMPs might not be what theorists originally thought. DAMA initially reported 60 proton-mass WIMPs based on the belief that the WIMPs collided with iodine atoms. But later data suggested that perhaps the WIMPs were hitting sodium atoms, implying a much lighter WIMP mass — lighter than other experiments had been optimally designed to detect. Yet another possibility: Maybe trace amounts of the metallic element thallium (much heavier atoms than either iodine or sodium) had been the WIMP targets. But a recent review of that proposal found once again that the DAMA results could not be reconciled with the absence of a signal in other experiments.

And now DAMA’s hope for vindication has been further dashed by a new underground experiment, this one in Spain. Scientists with the ANAIS collaboration have repeated the June-December method with sodium iodide, in an effort to reproduce DAMA’s results with the same method and materials. After three years of operation, the ANAIS team reports no sign of WIMPs.

To be fair, the no-WIMP conclusion relies on a lot of seriously sophisticated technical analysis. It’s not just a matter of counting light flashes. You have to collect rigorous data on the behavior of nine different sodium iodide modules. You have to correct for the presence of rare radioactive isotopes generated by cosmic ray collisions while the modules were still under construction. And then the statistical analysis needed to discern a winter-summer signal difference is not something you should try at home (unless you’re fully versed in things like the least-square periodogram or the Lomb-Scargle technique). Plus, ANAIS it still going, with plans to collect two more years of data before issuing a final analysis. So the judgment on DAMA’s WIMPs is not necessarily final.

Nevertheless, it doesn’t look good for WIMPs, at least for the WIMPs motivated by belief in supersymmetry.   

Sadly for SUSY fans, searches for WIMPs from space are not the only bad news. Attempts to produce WIMPs in particle accelerators have also so far failed. Dark matter might just turn out to consist of some other kind of subatomic particle.

If so, it would be a plot twist worthy of Agatha Christie, kind of like Poirot turning out to be the killer. For symmetry has long been physicists’ most reliable friend, guiding many great successes, from Einstein’s relativity theory to the standard model of particles and forces.

Still, failure to find SUSY particles so far does not necessarily mean they don’t exist. Supersymmetry just might be not as simple as it first seemed. And SUSY particles might just be harder to detect than scientists originally surmised. But if supersymmetry does turn out not to be so super, scientists might need to reflect on the ways that faith in symmetry can lead them astray. More