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Science

Galaxies without dark matter perplex astronomers

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This Hubble image captures a set of galaxies that are unusual because they seem not to have dark matter.Credit: NASA/ESA/P. van Dokkum, Yale Univ.

Astronomers think that galaxies cannot form without the gravitational pull of dark matter. So a trail of galaxies free of this mysterious material, with no obvious cause, would be a remarkable find. In a paper published in Nature on 18 May1, astronomers say they might have observed such a system — a line of 11 galaxies that don’t contain any dark matter, which could all have been created in the same ancient collision. But many of their peers are unconvinced that the claim is much more than a hypothesis.

This kind of system could be used to learn about how galaxies form, and about the nature of dark matter itself. “If proven right, this could certainly be exciting for galaxy formation. However, the jury is still out,” says Chervin Laporte, an astronomer at the University of Barcelona in Spain.

The finding centres on two galaxies described by Pieter van Dokkum at Yale University in New Haven, Connecticut, and his co-authors in 2018 and 2019. Their stars moved so slowly that the pull of dark matter was not needed to explain their orbits, so the team concluded that the galaxies contained no dark matter. The finding was controversial because the galaxies, named DF2 and DF4, seemed stable and different from the only other known dark-matter-free galaxies, which are new and short-lived, created in the arms of larger galaxies whose dark matter is being stripped by a neighbour. How DF2 and DF4 formed was a mystery.

Telltale trail

In the latest paper, van Dokkum’s team not only connects the two unusual galaxies, but says their properties are consistent with them being formed in a high-speed collision, eight billion years ago, that also spawned more such structures. “This single explanation explains so many odd things about these galaxies,” says van Dokkum.

The team borrowed its scenario from simulations originally created to explain unique features in larger-scale collisions between galaxy clusters. The researchers suggest that when two progenitor galaxies collided head on, their dark matter and stars would have sailed past each other; the dark matter would not have interacted, and the stars would have been too far apart to collide. But as the dark matter and stars sped on, gas in the space between the two galaxies’ stars would have crashed together, compacted and slowed down, leaving a trail of matter that later formed new galaxies with no dark matter.

Next, the researchers looked for such galaxies in the line between DF2 and DF4. They identified between three and seven new candidates for dark-matter-free galaxies, as well as strange, faint galaxies at either end, which could be the dark matter and stars remaining from the progenitor galaxies. “It was staring you in the face once you knew what to look for,” says van Dokkum.

If this picture proves to be true, it could help astronomers to understand how dark matter behaves, and to learn about the circumstances under which galaxies can form. Such a galactic collision might also be used as a “new laboratory” to understand whether dark matter interacts with itself, says Go Ogiya, an astronomer at Zhejiang University in Hangzhou, China.

Open questions

Although plausible, van Dokkum’s model describes just one of a number of ways that these galaxies could have been made, says Priyamvada Natarajan, an astrophysicist at Yale who is not a member of van Dokkum’s team. But it is intriguing and, crucially, makes testable predictions, she says.

Measurements of the precise distances and velocities of candidate galaxies could prove they are part of the same string and not just coincidentally along the same line of sight, says Michelle Collins, an astronomer at the University of Surrey in Guildford, UK. “For me, whether this is a real line or not is a big open question.”

Astronomers also need to measure the masses of the ghost galaxies at the ends of the line — the potential progenitor galaxies — to test whether they contain lots of dark matter, as the model predicts, adds Laporte.

Others question whether any exotic explanation is needed. Ignacio Trujillo, an astronomer at the Institute of Astrophysics of the Canary Islands in La Laguna, Spain, leads a team that proposes that DF2 and DF4 are closer to Earth than van Dokkum’s measurements suggest, and therefore contain more dark matter than was at first apparent.

Astronomers also need to see a reliable simulation showing that the scenario van Dokkum’s team describes is plausible, says Mireia Montes, an astronomer at the Space Telescope Science Institute in Baltimore, Maryland. “For now, there are a lot of assumptions, but those are not supported by any simulation,” she says.

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US

Sacramento goes dark in power outage, Legislature delayed

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SACRAMENTO, Calif. (AP) — A power outage in Sacramento on Thursday that left much of the city’s downtown area in the dark delayed the start of California’s Legislature.

Utility crews worked to replace a transformer and the outage delayed legislators from starting work for about half an hour.

The Sacramento Municipal Utilities District reported 650 customers were without power during the morning, a figure that likely represented thousands of people because multiple high-rise office buildings and the state Capitol were impacted. Many downtown traffic lights went dark.

The state Legislature had been scheduled to meet at 9 a.m. The outage delayed the start of the state Assembly until 9:30 a.m. The state Senate planned to meet in a legislative committee room in another building. The power was restored by late morning.

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Science

A collision strips dark matter, starts star formation

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Enlarge / The dark matter-poor galaxies are so diffuse that you can see right through them.

The Universe’s first galaxies are thought to have formed at sites where a lot of dark matter coalesced, providing the gravitational pull to draw in enough regular matter to create stars. And, to date, it’s impossible to explain the behavior of almost all the galaxies we’ve observed without concluding that they have a significant dark matter component.

Almost, but not all. Recently, a handful of galaxies have been identified that are dim and diffuse, and appear to have relatively little dark matter. For a while, these galaxies couldn’t be explained, raising questions about whether the observations had provided an accurate picture of their composition. However, researchers recently identified one way the galaxies could form: A small galaxy could be swallowed by a larger one that keeps the dark matter and spits out the stars.

Now, a second option has been proposed, based on the behavior of dark matter in a galaxy cluster. This model may explain a series of objects found near the dark matter-poor galaxies. And it may suggest that galaxy-like objects could be formed without an underlying dark matter component.

Bullet time

The galaxy cluster that’s the inspiration for this model is called the Bullet Cluster. First described in 2006, this huge grouping of galaxies is the product of a collision between two previously distinct clusters. Because dark matter doesn’t interact physically, the dark matter portion of each of the two clusters passed gracefully through the collision site and continued on its way. The regular matter, in contrast, experienced an actual collision, with shockwaves developing within the large amounts of gas that accompanied the galaxy clusters.

Observations of gravitational lensing indicated that most of the mass was with the dark matter, which had moved past the collision site. But most of the visible matter is still near where the collision initially took place. This method of separating regular and dark matter has held up well to further observations and modeling.

The new work relies on extending the mechanism involved in creating the Bullet Cluster down to the scale of individual galaxies. The physics works the same way: A collision slams normal matter into a messy collision driven by its interactions, while dark matter passes smoothly through the mess. It’s not clear how much of the regular matter structures can survive this sort of mess. But, because there can be a lot of gas present after the dark matter has moved on, it’s possible the regular matter can form structures that lack a dark matter component.

The new research applies this logic to the two best-established dark matter-free galaxies, called DF2 and DF4, which are dwarf galaxies that exist near a normal, large galaxy called NGC 1052.

This goes to 11

It’s easy to model collisions between dwarf galaxies that create a situation akin to the Bullet Cluster, with dark and regular matter separated. Collectively, these are referred to as “bullet dwarf” collisions. (Dwarf bullet would seem to be more descriptive, but that wasn’t chosen for some reason.)

But in this case, the researchers were able to put a lot of constraints on the model based on the physical situation around NGC 1052. One of those constraints was provided by NGC 1052, the large galaxy in the area. There’s no real reason to expect these sorts of galaxy collisions to occur near a large galaxy like that. Its presence in the area suggests that the proximity was central to the collision: One of the smaller galaxies involved in the collision was in orbit around NGC 1052.

Obviously, having both in orbit would make a collision more probable. But it would also mean that the dwarf galaxies wouldn’t have a combined speed that would create a sufficiently violent collision. So at least one of the galaxies would have to come in from outside the system and pick up speed while being drawn in toward NGC 1052.

The other major constraint they have is the existence of the two dark matter-poor galaxies, DF2 and DF4, as well as a sense of their relative motion. The relative motion allowed the researchers to trace the galaxies’ movements backward through time and conclude that any collision probably took place about 8 billion years ago, which is in good agreement with the age of some of the stars in DF2.

Models of the collision suggest that, in addition to DF2 and DF4, this collision should produce two dark matter-rich dwarf galaxies, and those should appear to be roughly along the line defined by DF2 and DF4. So the researchers looked in a catalog of objects for other dwarf galaxies in the region that might have emerged from the collision. Instead of four total objects, they found 11.

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Business

Golden arches to go dark in Russia as McDonald’s exits after 30 years

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May 16 (Reuters) – McDonald’s Corp (MCD.N) on Monday became one of the biggest global names to exit Russia, laying out plans to sell all its restaurants after operating for more than 30 years in the country following its invasion of Ukraine.

The world’s largest burger chain, which owns about 84% of its nearly 850 restaurants in Russia, will take a related non-cash charge of up to $1.4 billion.

McDonald’s had in March decided to close its restaurants in the country, including the iconic Pushkin Square location in central Moscow – a symbol of flourishing American capitalism in the dying embers of the Soviet Union.

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In the Russia of the early nineties, the burger chain became a way to sample Western food and spirit for millions of people, even though the cost of one burger was several times bigger than many city dwellers’ daily budgets.

“Some might argue that providing access to food and continuing to employ tens of thousands of ordinary citizens is surely the right thing to do,” Chief Executive Chris Kempczinski said in a letter to employees. “But it is impossible to ignore the humanitarian crisis caused by the war in Ukraine.”

Though a vast majority of the stores in Russia are closed, a few franchised stores have stayed open, cashing in on its skyrocketing popularity. It generated about 9%, or $2 billion, of its revenue from Russia and Ukraine last year.

A logo of the McDonald’s restaurant is seen in the window with a reflection of Kremlin’s tower in central Moscow, Russia March 9, 2022. REUTERS/Maxim Shemetov

Over the weekend, long, snaking queues were seen at the restaurant in Moscow’s Leningradsky Station, one of the capital’s only branches that has remained open, social media footage showed.

McDonald’s said it was looking to sell its restaurants in Russia to a local buyer, but will retain its trademarks.

“Given the circumstances of the sale, the financial challenges faced by potential Russian buyers, and the fact that McDonald’s will not license its brand name or identity, it is unlikely the sale price will be anywhere near the pre-invasion book value of the business,” Neil Saunders, managing director of GlobalData, said.

McDonald’s said it would ensure its 62,000 employees in Russia continue to be paid until the close of any transaction and that they have future jobs with any potential buyer.

After McDonald’s decision to close stores in March, several American brands including Starbucks Corp (SBUX.O), PepsiCo Inc (PEP.O) and Coca-Cola Co (KO.N) followed suit, scrambling to comply with sanctions and deal with threats from the Kremlin that foreign-owned assets may be seized. read more

“I would not be surprised to see other companies follow McDonald’s lead of exiting the market,” Edward Jones analyst Brian Yarbrough said.

Earlier in the day, French carmaker Renault (RENA.PA) said it would sell its majority stake in Avtovaz (AVAZI_p.MM) to a Russian science institute. read more

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Reporting by Uday Sampath and Deborah Sophia in Bengaluru; Editing by Sriraj Kalluvila and Arun Koyyur

Our Standards: The Thomson Reuters Trust Principles.

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Science

Ingenuity Mars Helicopter Went Silent, Leaving Anxious NASA Team in the Dark

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Late last week, NASA’s Ingenuity helicopter managed to reestablish its connection with the Perseverance rover following a brief communications disruption. The space agency says the looming winter is likely responsible and is making adjustments as a result.

On Thursday, Ingenuity—mercifully—sent a signal to Perseverance after the intrepid helicopter missed a scheduled communications session. It marked the first time since the pair landed together on Mars in February 2021 that Ingenuity has missed an appointment, according to NASA.

The team behind the mission believes that Ingenuity had entered into a low-power state to conserve energy, and it did so in response to the charge of its six lithium-ion batteries dropping below a critical threshold. This was likely due to the approaching winter, when more dust appears in the Martian atmosphere and the temperatures get colder. The dust blocks the amount of sunlight that reaches the helicopter’s solar array, which charges its batteries.

The Perseverance rover is on a mission to find evidence of ancient microbial life on Mars, while the rover’s much smaller companion, Ingenuity, became the first powered aircraft to lift off from the surface of another planet on April 19, 2021. The two robots share a communication line, with Perseverance relaying Ingenuity’s messages to Earth. Ingenuity uses small antennas to communicate with Perseverance, exchanging data that is then routed to the rover’s main computer and transferred to Earth through NASA’s Deep Space Network (a global array of radio antennas).

Ingenuity has an alarm that wakes the helicopter for its scheduled communication sessions with Perseverance. But on May 3, Ingenuity was a no-show for the scheduled daily data exchange after its field-programmable gate array lost power overnight, causing a reset of the helicopter’s onboard clock (the gate array manages Ingenuity’s operational state, switching its electronic systems on and off to conserve power). The Sun’s rays recharged Ingenuity’s batteries the following morning, but the helicopter’s clock was now out of sync with Perseverance’s clock. By the time Ingenuity was able to send out a signal, the rover was no longer listening.

Two days later, mission control set out to fix the pair’s communication issue by programming the rover to spend nearly the entirety of its 429th sol (a Martian day, which lasts slightly longer than a day on Earth) listening for the helicopter’s signal. Ingenuity’s call finally came in on May 5 at 11:45 a.m. local Mars time. Although brief, Ingenuity’s call reassured the team at NASA’s Jet Propulsion Laboratory that the helicopter’s battery was healthy and that the solar array was recharging its batteries.

Ingenuity wasn’t exactly built to withstand the harsh Martian winter nights, as the rotorcraft was designed to last only 30 sols on Mars. But the 19-inch tall (48 cm), 4-pound (1.8 kg) helicopter has gone far beyond its test flights, recently receiving an extension on its mission to assist Perseverance as it explores the Martian terrain. Ingenuity will now fly above the Martian surface, advising Perseverance’s controllers on the most ideal routes.

“We have always known that Martian winter and dust storm season would present new challenges for Ingenuity, specifically colder sols, an increase in atmospheric dust, and more frequent dust storms,” Teddy Tzanetos, Ingenuity team lead at JPL, said in a statement. “Every flight and every mile of distance flown beyond our original 30-sol mission has pushed the spacecraft to its limits each and every sol on Mars.”

For now, the team has put together a plan to help the tiny helicopter survive the looming winter. The newly issued commands “lower the point at which the helicopter energizes its heaters from when the battery falls below 5 degrees Fahrenheit (minus 15 degrees Celsius) to minus 40 degrees Fahrenheit (minus 40 degrees Celsius),” according to NASA, which added that the “helicopter then shuts down quickly, rather than consuming the battery charge with the heaters.” This should allow Ingenuity to accumulate battery charge during the day, which it can then use to survive the bitterly cold nights.

“Our top priority is to maintain communications with Ingenuity in the next few sols, but even then, we know that there will be significant challenges ahead,” Tzanetos said. “We are hopeful that we can accumulate battery charge in order to return to nominal operations and continue our mission into the weeks ahead.”

Even with the dropped call, Ingenuity still remains the little copter that could, surpassing expectations with a total of 28 flights logged on Mars. Hard to believe now, but the original plan was to have Ingenuity perform just five flights on the Red Planet.

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Science

Galactic Ballet Captured by State-of-the-Art Dark Energy Camera

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The interacting galaxy pair NGC 1512 and NGC 1510 take center stage in this image from the Dark Energy Camera, a state-of-the art wide-field imager on the Víctor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory, a Program of NSF’s NOIRLab. NGC 1512 has been in the process of merging with its smaller galactic neighbor for 400 million years, and this drawn-out interaction has ignited waves of star formation and warped both galaxies. Credit: Dark Energy Survey/DOE/FNAL/DECam/CTIO/NOIRLab/NSF/AURA, Image processing: T.A. Rector (University of Alaska Anchorage/NSF’s NOIRLab), J. Miller (Gemini Observatory/NSF’s NOIRLab), M. Zamani & D. de Martin (NSF’s NOIRLab)

DOE-funded Dark Energy Camera at NSF’s NOIRLab in Chile captures a pair of galaxies performing a gravitational duet.

The interacting galaxy pair NGC 1512 and NGC 1510 take center stage in this image from the US Department of Energy-fabricated Dark Energy Camera, a state-of-the-art wide-field 570-megapixel imager on the Víctor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory, a Program of NSF’s NOIRLab. NGC 1512 has been in the process of merging with its smaller galactic neighbor for 400 million years, and this drawn-out interaction has ignited waves of star formation.

The barred spiral galaxy NGC 1512 (left) and its diminutive neighbor NGC 1510 were captured in this observation (image at the top of the article) from the Víctor M. Blanco 4-meter Telescope. As well as revealing the intricate internal structure of NGC 1512, this image shows the wispy outer tendrils of the galaxy stretching out and appearing to envelop its tiny companion. The starry stream of light that connects the two galaxies is evidence of the gravitational interaction between them — a stately and graceful liaison that has been going on for 400 million years. NGC 1512 and NGC 1510’s gravitational interaction has affected the rate of star formation in both galaxies as well as distorting their shapes. Eventually, NGC 1512 and NGC 1510 will merge into one larger galaxy — a drawn-out example of galactic evolution.

A wider crop of the NGC 1512 image. Credit: Dark Energy Survey/DOE/FNAL/DECam/CTIO/NOIRLab/NSF/AURA, Image processing: T.A. Rector (University of Alaska Anchorage/NSF’s NOIRLab), J. Miller (Gemini Observatory/NSF’s NOIRLab), M. Zamani & D. de Martin (NSF’s NOIRLab)

These interacting galaxies lie in the direction of the constellation of Horologium in the southern celestial hemisphere and are around 60 million light-years from Earth. The wide field of view of this observation shows not only the intertwined galaxies, but also their star-studded surroundings. The frame is populated with bright foreground stars within the

An even wider crop of the NGC 1512 image. Credit: Dark Energy Survey/DOE/FNAL/DECam/CTIO/NOIRLab/NSF/AURA, Image processing: T.A. Rector (University of Alaska Anchorage/NSF’s NOIRLab), J. Miller (Gemini Observatory/NSF’s NOIRLab), M. Zamani & D. de Martin (NSF’s NOIRLab)

Large astronomical instruments such as DECam are custom-built masterpieces of optical engineering, requiring enormous effort from astronomers, engineers, and technicians before the first images can be captured. Funded by the US Department of Energy (DOE) with contributions from international partners, DECam was built and tested at DOE’s Fermilab, where scientists and engineers built a “telescope simulator” — a replica of the upper segments of the Víctor M. Blanco 4-meter Telescope — that allowed them to thoroughly test DECam before shipping it to Cerro Tololo in Chile.


DECam was created to conduct the Dark Energy Survey (DES), a six-year observing campaign (from 2013 to 2019) involving over 400 scientists from 25 institutions in seven countries. This international collaborative effort set out to map hundreds of millions of galaxies, detect thousands of supernovae, and discover delicate patterns of cosmic structure — all to provide much-needed details of the mysterious dark energy that is accelerating the expansion of the Universe. Today DECam is still used for programs by scientists from around the world continuing its legacy of cutting-edge science.



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