Saturday, May 04, 2024

SPACE

X-ray satellite XMM-newton sees ‘space clover' in a new light



NASA/GODDARD SPACE FLIGHT CENTER

Cloverleaf Odd Radio Circle XMM-Newton 

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THIS MULTIWAVELENGTH IMAGE OF THE CLOVERLEAF ORC (ODD RADIO CIRCLE) COMBINES VISIBLE LIGHT OBSERVATIONS FROM THE DESI (DARK ENERGY SPECTROSCOPIC INSTRUMENT) LEGACY SURVEY IN WHITE AND YELLOW, X-RAYS FROM XMM-NEWTON IN BLUE, AND RADIO FROM ASKAP (THE AUSTRALIAN SQUARE KILOMETER ARRAY PATHFINDER) IN RED.

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CREDIT: X. ZHANG AND M. KLUGE (MPE), B. KORIBALSKI (CSIRO)





Astronomers have discovered enormous circular radio features of unknown origin around some galaxies. Now, new observations of one dubbed the Cloverleaf suggest it was created by clashing groups of galaxies.

Studying these structures, collectively called ORCs (odd radio circles), in a different kind of light offered scientists a chance to probe everything from supersonic shock waves to black hole behavior.

“This is the first time anyone has seen X-ray emission associated with an ORC,” said Esra Bulbul, an astrophysicist at the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, who led the study. “It was the missing key to unlock the secret of the Cloverleaf’s formation.”

A paper describing the results was published in Astronomy and Astrophysics Letters on April 30.

A Serendipitous Discovery

Until 2021, no one knew ORCs existed. Thanks to improved technology, radio surveys became sensitive enough to pick up such faint signals. Over the course of a few years, astronomers discovered eight of these strange structures scattered randomly beyond our galaxy. Each is large enough to envelop an entire galaxy –– sometimes several.

“The power needed to produce such an expansive radio emission is very strong,” Bulbul said. “Some simulations can reproduce their shapes but not their intensity. No simulations explain how to create ORCs.”

When Bulbul learned ORCs hadn’t been studied in X-ray light, she and postdoctoral researcher Xiaoyuan Zhang began poring over data from eROSITA (Extended Roentgen Survey with an Imaging Telescope Array), an orbiting German/Russian X-ray telescope. They noticed some X-ray emission that seemed like it could be from the Cloverleaf, based on less than 7 minutes of observation time.

That gave them a strong enough case to assemble a larger team and secure additional telescope time with XMM-Newton, an ESA (European Space Agency) mission with NASA contributions.

“We were allotted about five-and-a-half hours, and the data came in late one evening in November,” Bulbul said. “I forwarded it to Xiaoyuan, and he came into my office the next morning and said, ‘Detection,’ and I just started cheering!”

“We really got lucky,” Zhang said. “We saw several plausible X-ray point sources close to the ORC in eROSITA observations, but not the expanded emission we saw with XMM-Newton. It turns out the eROSITA sources couldn’t have been from the Cloverleaf, but it was compelling enough to get us to take a closer look.”

Gallivanting Galaxies

The X-ray emission traces the distribution of gas within the group of galaxies like police tape around a crime scene. By seeing how that gas has been disturbed, scientists determined that galaxies embedded in the Cloverleaf are actually members of two separate groups that drew close enough together to merge. The emission’s temperature also hints at the number of galaxies involved.

When galaxies join, their higher combined mass increases their gravity. Surrounding gas begins to fall inward, which heats up the infalling gas. The greater the system’s mass, the hotter the gas becomes.

Based on the emission’s X-ray spectrum, it’s around 15 million degrees Fahrenheit, or between 8 and 9 million degrees Celsius. “That measurement let us deduce that the Cloverleaf ORC is hosted by around a dozen galaxies that have gravitated together, which agrees with what we see in deep visible light images,” Zhang said.

The team proposes the merger produced shock waves that accelerated particles to create radio emission.

“Galaxies interact and coalesce all the time,” said Kim Weaver, the NASA project scientist for XMM-Newton at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, who was not involved in the study. “But the source of the accelerated particles is unclear. One fascinating idea for the powerful radio signal is that the resident supermassive black holes went through episodes of extreme activity in the past, and relic electrons from that ancient activity were reaccelerated by this merging event.”

While galaxy group mergers are common, ORCs are very rare. And it’s still unclear how these interactions can produce such strong radio emissions.

“Mergers make up the backbone of structure formation, but there’s something special in this system that rockets the radio emission,” Bulbul said. “We can’t tell right now what it is, so we need more and deeper data from both radio and X-ray telescopes.”

The team solved the mystery of the nature of the Cloverleaf ORC, but also opened up additional questions. They plan to study the Cloverleaf in more detail to tease out answers. 

“We stand to learn a lot from more thorough observations because these interactions take in all kinds of science,” Weaver says. “You’ve pretty much got everything that we deal with in the cosmos put together in this little package. It’s like a mini universe.”

For more information on ESA’s XMM-Newton mission, visit: https://science.nasa.gov/mission/xmm-newton/


Webb telescope probably didn’t find life on an exoplanet — yet


Claims of biosignature gas detection were premature



UNIVERSITY OF CALIFORNIA - RIVERSIDE

Hycean world 

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ARTIST RENDERING OF THE VIEW ON A HYCEAN WORLD.

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CREDIT: SHANG-MIN TSAI/UCR





Recent reports of NASA’s James Webb Space Telescope finding signs of life on a distant planet understandably sparked excitement. A new study challenges this finding, but also outlines how the telescope might verify the presence of the life-produced gas.

The UC Riverside study, published in the Astrophysical Journal Letters, may be a disappointment to extraterrestrial enthusiasts but does not rule out the near-future possibility of discovery.

In 2023 there were tantalizing reports of a biosignature gas in the atmosphere of planet K2-18b, which seemed to have several conditions that would make life possible. 

Many exoplanets, meaning planets orbiting other stars, are not easily comparable to Earth. Their temperatures, atmospheres, and climates make it hard to imagine Earth-type life on them. 

However, K2-18b is a bit different. “This planet gets almost the same amount of solar radiation as Earth. And if atmosphere is removed as a factor, K2-18b has a temperature close to Earth’s, which is also an ideal situation in which to find life,” said UCR project scientist and paper author Shang-Min Tsai. 

K2-18b’s atmosphere is mainly hydrogen, unlike our nitrogen-based atmosphere. But there was speculation that K2-18b has water oceans, like Earth. That makes K2-18b a potentially “Hycean” world, which means a combination of a hydrogen atmosphere and water oceans. 

Last year, a Cambridge team revealed methane and carbon dioxide in the atmosphere of K2-18b using JWST – other elements that could point to signs of life. 

“What was icing on the cake, in terms of the search for life, is that last year these researchers reported a tentative detection of dimethyl sulfide, or DMS, in the atmosphere of that planet, which is produced by ocean phytoplankton on Earth,” Tsai said. DMS is the main source of airborne sulfur on our planet and may play a role in cloud formation.

Because the telescope data were inconclusive, the UCR researchers wanted to understand whether enough DMS could accumulate to detectable levels on K2-18b, which is about 120 light years away from Earth. As with any planet that far away, obtaining physical samples of atmospheric chemicals is impossible.

“The DMS signal from the Webb telescope was not very strong and only showed up in certain ways when analyzing the data,” Tsai said. “We wanted to know if we could be sure of what seemed like a hint about DMS.”

Based on computer models that account for the physics and chemistry of DMS, as well as the hydrogen-based atmosphere, the researchers found that it is unlikely the data show the presence of DMS. “The signal strongly overlaps with methane, and we think that picking out DMS from methane is beyond this instrument’s capability,” Tsai said. 

However, the researchers believe it is possible for DMS to accumulate to detectable levels. For that to happen, plankton or some other life form would have to produce 20 times more DMS than is present on Earth. 

Detecting life on exoplanets is a daunting task, given their distance from Earth. To find DMS, the Webb telescope would need to use an instrument better able to detect infrared wavelengths in the atmosphere than the one used last year. Fortunately, the telescope will use such an instrument later this year, revealing definitively whether DMS exists on K2-18b.

"The best biosignatures on an exoplanet may differ significantly from those we find most abundant on Earth today. On a planet with a hydrogen-rich atmosphere, we may be more likely to find DMS made by life instead of oxygen made by plants and bacteria as on Earth,” said UCR astrobiologist Eddie Schwieterman, a senior author of the study. 

Given the complexities of searching far-flung planets for signs of life, some wonder about the researchers continued motivations. 

“Why do we keep exploring the cosmos for signs of life? Imagine you’re camping in Joshua Tree at night, and you hear something. Your instinct is to shine a light to see what’s out there. That’s what we’re doing too, in a way,” Tsai said. 

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