369: Scientists discover the fastest stars ever seen in the Milky Way



Astronomers discovered a new population of ultra-fast-moving stars, including the fastest ‘runaway’ star ever seen in our galaxy.

A red ‘runaway’ star appears to blaze with fire as it exits its original star system in the Flaming Star nebula (Image credit: NASA/JPL-Caltech/UCLA)

Astronomers have detected the fastest runaway star ever seen in the Milky Way galaxy — the husk of a star launched at blistering speeds from a gigantic cosmic explosion.

The white dwarf, named J0927, was spotted hurtling through space at a stunning 5.112 million miles per hour (8,226,967 kilometers per hour).

Called a hypervelocity star because its speed will one day enable it to entirely escape the gravitational pull of the Milky Way, J0927 was spotted alongside three other fast-moving stars, all of which are thought to be the results of a Type Ia supernova — one of the most violent explosions in the universe. The researchers published their findings June 6 on the preprint server arXiv, and the findings have not yet been peer-reviewed.

Type Ia supernovas occur when two stars, one of them the collapsed husk of a star called a white dwarf, fall into orbit around each other. This causes the white dwarf to strip hydrogen from the star it is spiraling around, creating a runaway reaction that ends in a gigantic thermonuclear explosion.

But a simple star explosion isn’t enough to launch stars at this speed. Astronomers suspect that hypervelocity stars are sent flying by a special kind of Type Ia supernova called a dynamically driven double-degenerate double-detonation (D6) supernova.

In D6 supernovas, two white dwarf stars spiral each other, one stripping the other of any remaining layers of helium from its surface. This process produces so much energy on the helium-snatching white dwarf’s surface that it kick-starts nuclear fusion in the husk once more, sending a shock wave deep into its core that causes it to detonate.

“If a significant fraction of Type Ia supernovae produce a D6 star, the galaxy has likely launched more than 10 million of them into intergalactic space,” the researchers wrote in the study. “An interesting corollary is that there should be large numbers of faint, nearby D6 stars launched from galaxies all throughout the local volume passing through the solar neighborhood.”

Despite the apparent abundance of these powerful supernovas, evidence for them and the white dwarfs they fire like bullets remains hard to find. To search for some candidates, the researchers turned to the Gaia star catalog, an ongoing project with the goal of creating the most detailed star map of our galaxy ever made.

From the Gaia data, the astronomers spotted the white dwarfs, confirming with follow-up observations of their chemical compositions (almost entirely oxygen and carbon) that the runaway white dwarfs were products of an explosion that stripped away their helium and hydrogen.

Measurements of the white dwarfs revealed that J0927 was the fastest runaway star ever observed in our galaxy, beating the previous record of 4,921,200 mph (7,919,904 km/h) held by the white dwarf D6-1. An additional white dwarf observed in the new study also grabbed the title of second-fastest star ever observed in our galaxy.

The researchers estimate that D6 supernovas might account for half of all Type Ia supernovas, but to know for certain, they will have to locate even more runaway stars streaking through space.

“There is now a sizable population of hypervelocity stars associated with thermonuclear supernovae,” the researchers wrote. “Modeling this population will ultimately make it possible to infer the formation rate of thermonuclear runaways and ultimately, the fraction of Type Ia supernovae formed through the double-degenerate channel.”

Live Science
published 16.06.2023

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321: Repeated signals from the center of the Milky Way could be aliens saying hello, new study claims



A new search for extraterrestrial life has scientists looking inward — toward the center of our galaxy.

A hypothetical alien craft transmits radio signals into space. Scientists are on the hunt for signals like these. (Image credit: Breakthrough Listen / Danielle Futselaar)

Could intelligent aliens be lurking at the heart of the Milky Way?

A new search for extraterrestrial life aims to find out by listening for radio pulses from the center of our galaxy. Narrow-frequency pulses are naturally emitted by stars called pulsars, but they’re also used deliberately by humans in technology such as radar. Because these pulses stand out against the background radio noise of space, they’re an effective way of communicating across long distances — and an appealing target to listen for when searching for alien civilizations.

Scientists described the alien-hunting strategy in a new study, published May 30 in The Astronomical Journal. Researchers led by Cornell University graduate student Akshay Suresh developed software to detect these repetitive frequency patterns and tested it on known pulsars to be sure it could pick up the narrow frequencies. These frequency ranges are very small, at about a tenth of the width of frequencies used by a typical FM radio station. The researchers then searched data from the Green Bank Telescope in West Virginia using the method.

“Until now, radio SETI has primarily dedicated its efforts to the search for continuous signals,” study coauthor Vishal Gajjar of the SETI Institute, a nonprofit organization dedicated to the search for intelligent life in the universe, said in a statement. “Our study sheds light on the remarkable energy efficiency of a train of pulses as a means of interstellar communication across vast distances. Notably, this study marks the first-ever comprehensive endeavor to conduct in-depth searches for these signals.”

The researchers are listening in to the middle of the Milky Way because it is dense with stars and potentially habitable exoplanets. What’s more, if intelligent aliens at the core of the Milky Way wanted to reach out to the rest of the galaxy, they could send signals sweeping across a wide array of planets, given their privileged position at the center of the galaxy. Using narrow bandwidths and repeated patterns would be a prime way for aliens to reveal themselves, as such a combination is extremely unlikely to occur naturally, study co-author Steve Croft, a project scientist with the Breakthrough Listen program, said in a separate statement.

The method uses an algorithm that can search through 1.5 million telescope data samples in 30 minutes. Though researchers did not find any telltale signs in their first search, they say that the speed of the algorithm will help improve searches in the future.

“Breakthrough Listen captures huge volumes of data, and Akshay’s technique provides a new method to help us search that haystack for needles that could provide tantalizing evidence of advanced extraterrestrial life forms,” Croft said.

Live Science
published 01.06.2023

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