Astronomy

To leave a lasting trail, meteors need to aim low. A new survey of shooting stars shows that meteors that blaze through 90 kilometers up in the sky leave a persistent afterglow, unlike those that burn up at greater heights.

Meteors are normally blink-and-you’ll-miss-it events. A particle of space dust leaves a fiery trail of light as it zips through the atmosphere, and then it’s gone. But sometimes, a meteor leaves a lingering afterglow. Astronomers have noted these persistent trains for more than a century, but questions remained about their origins. More

The star marking true north is a good deal heavier than we thought.

The North Star is 5.1 times as massive as the sun, astronomers report in work submitted July 12 to arXiv.org. That value, calculated from the motion of a much fainter star that orbits the luminary, is nearly 50 percent heavier than a recent estimate of 3.45 solar masses.

Mass profoundly affects stellar life: The more mass a star has, the faster it burns its fuel and the sooner it dies. The earlier mass estimate had suggested that the North Star, also known as Polaris, is roughly 100 million years old (SN/12/2/16). The new estimate means the star formed more recently than this, but no one has yet calculated a revised age. More

For the first time, astronomers have spotted a middleweight black hole in the nearby universe. The discovery could help solve the riddle of how even heftier black holes form and grow up with their host galaxies.

The black hole, which sits about 16,000 light-years from Earth in the center of star cluster Omega Centauri, is at least 8,200 times as massive as the sun, putting it squarely in a rare category of intermediate-mass black holes, researchers report July 10 in Nature. More

Keep your eyes on the night sky this summer, scanning for the constellation Corona Borealis, and if you are lucky, you may glimpse what appears to be a new star winking on in the dark.

The brightening point of light will not be a new star, but a nova eruption about 3,000 light-years from Earth. There, a white dwarf star orbiting a red giant tears material from its larger companion. When enough mass collects on the white dwarf’s surface, the rising pressure and temperature will trigger a blast that can be seen from Earth with the naked eye — but for only a few days to a week. More

Supermassive black holes at the hearts of active galaxies may be churning out a lot of the universe’s high-energy neutrinos.

Two teams using data from IceCube, the world’s premier neutrino observatory located in Antarctica, have independently identified a common type of these active galaxies, called Seyfert galaxies, as likely neutrino producers. These findings, reported in Physical Review Letters and arXiv.org, bolster some astronomers’ view that the cores of such active galaxies could churn out the majority of the cosmic neutrinos seen streaming across the universe. More

Within the dusty cloud left behind by supernova 1987A, the most famous stellar explosion in modern history, astronomers have found compelling evidence for a long-sought neutron star.

NASA’s James Webb Space Telescope has spied indirect hints of a powerful source of X-rays — likely some type of neutron star — coming from the core of the supernova remnant, researchers report February 22 in Science. The findings are part of a 37-year-old quest to determine what happened in the aftermath of the closest supernova in nearly 400 years and could provide insights into how a neutron star behaves mere decades after its birth.

“Supernova 1987A is truly a unique laboratory to study supernovas,” astronomer Patrick Kavanagh said February 17 in a news conference at the American Association for the Advancement of Science meeting in Denver. It’s “the gift that keeps on giving, with new observations continually yielding new discoveries,” said Kavanagh, of Maynooth University in Ireland.

It’s rare for scientists to have observations of a giant star before it explodes in a supernova — but they got lucky with supernova 1987A. On the left is the blue supergiant before the explosion. On the right is the explosion itself.David Malin, AAT

On February 23, 1987, telescopes around the world got a front-row seat to a spectacular supernova in the Large Magellanic Cloud, a companion galaxy to the Milky Way (SN: 2/8/17). Such explosions occur when a star at least eight times the mass of the sun dies. Located at the astronomically close distance of 160,000 light-years, supernova 1987A, as it came to be known, was visible with the naked eye in the night sky for months afterward. The energetic explosion generated tremendous amounts of neutrinos, a handful of which ended up in detectors on Earth. It was the first time such ghostly particles had been seen coming from beyond the solar system.

Since then, scientists have wondered whether the iron core of the blue supergiant star that led to 1987A collapsed into an ultradense neutron star or shrank all the way down to a black hole. The fact that neutrinos escaped the event favors the neutron star possibility, but whatever was left behind has yet to be spotted. That’s partly because the original star’s outer layers, now traveling away from the explosion at 10,000 kilometers per second, create a thick haze of dust that obscures the area. More

Circling around a pulsar in our galaxy is a mysterious entity that is either a very heavy neutron star, one of the lightest black holes ever discovered, or an exotic and never-before-seen quasi-stellar object.

The new finding comes from the MeerKAT Radio Telescope in South Africa, which carefully monitored 13 millisecond pulsars in a dense cluster of stars 40,000 light years from Earth. These pulsars are a type of neutron star that quickly spin, rotating in fractions of a second, while sending out powerful beams of radiation like a cosmic lighthouse. More

The biography of our home galaxy may be due for some revisions. That’s because a bar-shaped collection of stars at the center of the Milky Way appears to be much younger than expected.

The bar is a prominent feature of our galaxy (SN: 6/25/21). It spans thousands of light-years and links the galaxy’s spiraling arms of stars, making them resemble streams of water coming from a spinning lawn sprinkler. In computer simulations of the Milky Way’s evolution, the bar tends to form early in the galaxy’s roughly 13-billion-year lifetime. But the ages and locations of metal-rich stars suggest the bar finished forming just a few billion years ago, researchers report. The study, submitted November 28 to arXiv.org, is in press at Astronomy & Astrophysics Letters.

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“These metal-rich stars are basically like fossil records of ancient stars that are telling the story of our home galaxy,” says Samir Nepal, an astrophysicist at the Leibniz Institute for Astrophysics Potsdam in Germany.

Stars with large proportions of metal elements are built from the remnants of stars that have since exploded, ejecting the metals they forged from lighter elements. Those spewed metals enrich the materials in the core of galaxies like the Milky Way, which is why a new generation of metal-rich stars can form only deep inside galaxies. The spinning bar at the center of the Milky Way then scattered some of those stars throughout our galaxy.

Using data from the European Space Agency’s Gaia space telescope, Nepal and colleagues reconstructed the development of the Milky Way bar through its influence on the distribution of metal-rich stars (SN: 5/9/18). They inferred the bar’s history, just as you might deduce where the batters stand in a baseball game by looking at the flight of the balls they hit, even if you can’t see home plate.

In tracking the ages of the metal-rich stars, the researchers identified a burst of star formation in the central part of the galaxy that petered out about 3 billion years ago. The downturn seems to mark the end of the Milky Way bar’s developmental phase, the researchers report. After that burst, they say, the inflow of new material into the bar probably dropped off substantially. That suggests the bar we see today is a stable feature that’s about 10 billion years younger than the galaxy as a whole.

The new insights about the metal-rich stars “are like the tip of the iceberg” of data coming from the Gaia telescope, says astrophysicist Cristina Chiappini, also with the Leibniz Institute for Astrophysics Potsdam. Assuming the revised age estimate of the bar is confirmed, future models of the galaxy’s evolution will have to account for why the bar developed so late.

The study has broader implications than correcting the history of our galaxy, says Ortwin Gerhard, an astrophysicist at the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, who was not involved in the research. “The possibility of detailed observations of the motions and chemical abundances of stars in the Milky Way, particularly based on [data] from the Gaia satellite,” he says, means we can “expect to learn about the evolution of bars [in other galaxies] generally by studying the bar in the Milky Way.” More