| Title | Astronomers Witnessed the Birth of a Supermassive Magnetar Following a Kilonova | |
| Date | Thursday November 19 2020, @09:53PM | |
| Author | Fnord666 | |
| Topic | ||
| from the sounds-like-a-new-supervillian dept. | ||
NASA announces the Hubble Space Telescope captured images of the source of a Gamma-ray Burst.
Long ago and far across the universe, an enormous burst of gamma rays unleashed more energy in a half-second than the Sun will produce over its entire 10-billion-year lifetime. In May of 2020, light from the flash finally reached Earth and was first detected by NASA's Neil Gehrels Swift Observatory. Scientists quickly enlisted other telescopes — including NASA's Hubble Space Telescope, the Very Large Array radio observatory, the W. M. Keck Observatory, and the Las Cumbres Observatory Global Telescope network — to study the explosion's aftermath and the host galaxy. It was Hubble that provided the surprise.
Yes, a kilonova, a merger of neutron stars.
Based on X-ray and radio observations from the other observatories, astronomers were baffled by what they saw with Hubble: the near-infrared emission was 10 times brighter than predicted. These results challenge conventional theories of what happens in the aftermath of a short gamma-ray burst. One possibility is that the observations might point to the birth of a massive, highly magnetized neutron star called a magnetar.
"These observations do not fit traditional explanations for short gamma-ray bursts," said study leader Wen-fai Fong of Northwestern University in Evanston, Illinois. "Given what we know about the radio and X-rays from this blast, it just doesn't match up. The near-infrared emission that we're finding with Hubble is way too bright. In terms of trying to fit the puzzle pieces of this gamma-ray burst together, one puzzle piece is not fitting correctly."
Without Hubble, the gamma-ray burst would have appeared like many others, and Fong and her team would not have known about the bizarre infrared behavior. "It's amazing to me that after 10 years of studying the same type of phenomenon, we can discover unprecedented behavior like this," said Fong. "It just reveals the diversity of explosions that the universe is capable of producing, which is very exciting."
"There are more things in the heavens than are dreamt of in your astrophysics."
Neutron star mergers are very rare but are extremely important because scientists think that they are one of the main sources of heavy elements in the universe, such as gold and uranium.
Accompanying a short gamma-ray burst, scientists expect to see a "kilonova" whose peak brightness typically reaches 1,000 times that of a classical nova. Kilonovae are an optical and infrared glow from the radioactive decay of heavy elements and are unique to the merger of two neutron stars, or the merger of a neutron star with a small black hole.
Magnetic Monster?
Fong and her team have discussed several possibilities to explain the unusual brightness that Hubble saw. While most short gamma-ray bursts probably result in a black hole, the two neutron stars that merged in this case may have combined to form a magnetar, a supermassive neutron star with a very powerful magnetic field.
More?
If the extra brightness came from a magnetar that deposited energy into the kilonova material, then within a few years, the team expects the ejecta from the burst to produce light that shows up at radio wavelengths. Follow-up radio observations may ultimately prove that this was a magnetar, and this may explain the origin of such objects.
"With its amazing sensitivity at near-infrared wavelengths, Hubble really sealed the deal with this burst," explained Fong. "Amazingly, Hubble was able to take an image only three days after the burst. Through a series of later images, Hubble showed that a source faded in the aftermath of the explosion. This is as opposed to being a static source that remains unchanged. With these observations, we knew we had not only nabbed the source, but we had also discovered something extremely bright and very unusual. Hubble's angular resolution was also key in pinpointing the position of the burst and precisely measuring the light coming from the merger."
Not bad for a satellite telescope that should be retired.
The team's findings appear in an upcoming issue of The Astrophysical Journal.
In many places already, picking the Smithsonian Magazine one for the high density of links, arxiv included.
This year, astronomers witnessed a cosmic spectacle when two neutron stars—the dense remains of collapsing stars—crashed into each other billions of lightyears away. Their gargantuan collision lit up the galaxy with a flash and gave rise to a magnetar—a supermassive star with a hyper-powerful magnetic field. Astronomers have known about magnetars, but this event marks the first time they've ever witnessed one being born...
Using remarkably powerful equipment, including the Hubble Space Telescope and the Swift Observatory, the scientists observed a quick flash of light on May 22. The stars' collision certainly didn't occur that night—instead, it occurred 5.47 billion years ago, and its light had just reached Earth, according to a press release.
The team observed a quick flash of gamma radiation, the result of the stars crashing and sending space matter blasting through the galaxy to settle among the stars. Then came the long-burning glow of a kilonova—a colossal explosion that produces heavy elements like gold and platinum—as the space dust swirled around the newly formed magnetar, reports Live Science.
The explosion released more energy in half a second than the sun emits over ten billion years, according to another press release.
But the scientists noticed something even more bewildering: The flash emitted ten times the average amount of infrared light, reports Meghan Bartels for Space.com. The findings will be published in The Astrophysical Journal and are currently available on the pre-print server arXiv.org.
"When two neutron stars merge, the most common predicted outcome is that they form a heavy neutron star that collapses into a black hole within milliseconds or less," lead author Wen-fai Fong, an astrophysicist at Northwestern University, says in a press release.
"Our study shows that it's possible that, for this particular short gamma-ray burst, the heavy object survived," Fong says. "Instead of collapsing into a black hole, it became a magnetar: A rapidly spinning neutron star that has large magnetic fields, dumping energy into its surrounding environment and creating the very bright glow that we see."
The spinning magnetar transferred a remarkable amount of energy to the debris created by the collision, heating the material up and generating a bright glow, Richard A. Lovett for Cosmos.
Artist rendition on youtube.
Original Submission #1 Original Submission #2
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