Astronomy

An examination of the iconic Griffith Observatory, which has appeared in scores of films throughout the history of Hollywood.

Breakdancing will hit the global stage at the 2024 Summer Olympic Games in Paris, and this physicist is excited to break down the science

Eventually, all galaxies, including our own Milky Way, will meet their end. But how do galaxies die? If you're in the mood to destroy an entire galaxy, you have several options, depending on your desired level of destructiveness.

In the coming decades, NASA and China intend to send the first crewed missions to Mars. Given the distance involved and the time it takes to make a single transit (six to nine months), opportunities for resupply missions will be few and far between. As a result, astronauts and taikonauts will be forced to rely on local resources to meet their basic needs – a process known as in-situ resource utilization (ISRU). For this reason, NASA and other space agencies have spent decades scouting for accessible sources of liquid water.

Finding this water is essential for future missions and scientific efforts to learn more about Mars’s past, when the planet was covered by oceans, rivers, and lakes that may have supported life. In 2018, using ground-penetrating radar, the ESA’s Mars Express orbiter detected bright radar reflections beneath the southern polar ice cap that were interpreted as a lake. However, a team of Cornell researchers recently conducted a series of simulations that suggest there may be another reason for these bright patches that do not include the presence of water.

The research team was led by Daniel Lalich, a research associate at the Cornell Center for Astrophysics and Planetary Science (CCAPS). She was joined by Alexander G. Hayes, a Jennifer and Albert Sohn Professor, the Director of CCAPS, and the Principal Investigator of the Comparative Planetology & Solar System Exploration (COMPASSE), and Valerio Poggiali, a CCAPS Research Associate. Their paper that describes their findings, “Small Variations in Ice Composition and Layer Thickness Explain Bright Reflections Below Martian Polar Cap without Liquid Water,” appeared on June 7th in the journal Science Advances.

When the first robotic probes began making flybys of Mars in the 1960s, the images they acquired revealed surface features common on Earth. These included flow channels, river valleys, lakebeds, and sedimentary rock, all of which form in the presence of flowing water. For decades, orbiters, landers, and rovers have explored Mars’ surface, atmosphere, and climate to learn more about how and when much of this surface water was lost. In recent years, this has led to compelling evidence that what remains could be found beneath the polar ice caps today.

The most compelling evidence was obtained by the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) instrument aboard the Mars Express orbiter. This instrument was designed by NASA and the Italian Space Agency (ASI) to search for water on the Martian surface and down to depths of about 5 km (3 mi). The radar returns indicated that the bright patches could be caused by layered deposits composed of water, dry ice, and dust. These South Polar Layered Deposits (SPLD) are thought to have formed over millions of years as Mars’ axial tilt changed.

Subsequent research by scientists at NASA’s Jet Propulsion Laboratory (JPL) revealed dozens of other highly reflective sites beneath the surface. The implications of these findings were tremendous, not just for crewed missions but also for astrobiology efforts. In addition to being a potential source of water for future missions, it was also theorized that microbial life that once existed on the surface might be found there today. However, the findings were subject to debate as other viable explanations were offered.

While the same bright radar reflections have detected subglacial lakes on Earth (such as Lake Vostok under the East Antarctic Ice Sheet), Mars’s temperature and pressure conditions are very different. To remain in a liquid state, the water would need to be very briny, loaded with exotic minerals, or above an active magma chamber – none of which have been detected. As Lalich said in a recent interview with the Cornell Chronicle:

“I can’t say it’s impossible that there’s liquid water down there, but we’re showing that there are much simpler ways to get the same observation without having to stretch that far, using mechanisms and materials that we already know exist there. Just through random chance you can create the same observed signal in the radar.”

In a previous study, Lalich and his colleagues used simpler models to demonstrate that these bright radar signals could result from tiny variations in the thickness of the layers. These variations would be indiscernible to ground-penetrating radar and could lead to constructive interference between radar waves, producing reflections that vary in intensity and variability – like those observed across the SPLD. For their latest study, the team simulated 10,000 layering scenarios with 1,000 variations in the ice thickness and dust content of the layered deposits.

Their simulations also excluded any of the unusual conditions or exotic materials that would be necessary for liquid water. These simulations produced bright subsurface signals consistent with observations made by the MARSIS instrument. According to Lalich, these findings strongly suggest that he and his colleagues were correct in suspecting radar interference. In essence, radar waves bouncing off of layers too close together for the instrument to resolve may have combined, amplifying their peaks and troughs and appearing much brighter.

The team is not prepared to rule out the possibility that future missions with more sophisticated instruments could find definitive evidence of water. However, Lalich suspects that the case for liquid water (and potential life) on Mars may have ended decades ago. “This is the first time we have a hypothesis that explains the entire population of observations below the ice cap, without having to introduce anything unique or odd. This result where we get bright reflections scattered all over the place is exactly what you would expect from thin-layer interference in the radar. The idea that there would be liquid water even somewhat near the surface would have been really exciting. I just don’t think it’s there.”

If so, future missions may be forced to melt polar ice deposits and permafrost to get drinking water or possibly chemical reactions involving hydrazine (a la Mark Watney). In addition, astrobiology efforts may once again be placed on the back burner as they were when the Viking Landers failed to find conclusive evidence of biosignatures in 1976. But as we’ve learned, Mars is full of surprises. While the results of the Viking biological experiments were disappointing, these same missions provided some of the most compelling evidence that water once flowed on Mars’ surface.

Artist’s impression of water under the Martian surface. If underground aquifers exist, the implications for human exploration and eventual settlement of the Red Planet would be far-reaching. Credit: ESA

Moreover, scientists once suspected that the Red Planet was geologically dead, but data obtained by NASA’s InSight Lander showed that it is actually “slightly alive.” This included evidence that hot magma still flows deep in the planet’s interior and that a massive magma plume still exists beneath the Elysium Planitia region, which may have caused a small eruption just 53,000 years ago (the most recent in Martian history). Perhaps the same will hold true for briny patches of liquid water around the poles and the equatorial region.

With any luck, some of these patches may even house countless microorganisms that could be related to life on Earth. How cool would that be?

Further Reading: Cornell Chronicle, Science Advances

The post Don't Get Your Hopes Up for Finding Liquid Water on Mars appeared first on Universe Today.

What is that light in the sky?

Pandora's Cluster of Galaxies

A US military program led by DARPA is modifying the stimulant drug dextroamphetamine so it can be switched on or off in the brain using near-infrared light, avoiding risks like addiction

A US military program led by DARPA is modifying the stimulant drug dextroamphetamine so it can be switched on or off in the brain using near-infrared light, avoiding risks like addiction

A discarded Japanese rocket was recently imaged up close by the ADRAS-J mission.

A SpaceX rocket suffered a last-second abort during the attempted launch of 22 Starlink internet satellites from Florida on Friday (June 14).

Following a technical error in November 2023, NASA's deep-space explorer has resumed full science operations.

Strangely, the Star Trek: Discovery ship's far-future fate was revealed in 2018 'Short Trek' episode 'Calypso'.

The James Webb Space Telescope (JWST) has just increased the number of known distant supernovae by tenfold. This rapid expansion of astronomers’ catalog of supernovae is extremely valuable, not least because it improves the reliability of measurements for the expansion of the universe.

“Webb is a supernova discovery machine,” said Christa DeCoursey of the Steward Observatory and the University of Arizona at a press conference earlier this week. “The sheer number of detections plus the great distances to these supernovae are the two most exciting outcomes from our survey.”

JWST’s advantage over previous surveys is its specialty in infrared wavelengths. As the universe expands, the light coming from distant objects gets stretched, “redshifting” the light to longer wavelengths. Most of the light from the early universe, therefore, reaches us in infrared.

That has allowed the telescope to discover a host of new supernovae in distant galaxies, some of which are the furthest ever seen. Supernovas are transient objects – they’re exploding stars that change and fade over time – so catching them happening at such great distances is exciting.

Previously, the most distant supernova fell about the redshift 2 mark (3.3 billion years into the Universe’s life). The new record holder just discovered by JWST has a redshift of 3.6, meaning it exploded just 1.8 billion years after the Big Bang.

Closeups of three out of the 80 transients discovered by JWST, where a change of brightness was observed between 2022 and 2023. NASA, ESA, CSA, STScI, Christa DeCoursey (University of Arizona), JADES Collaboration

Of the 80 new objects discovered, several were type 1a supernovae. These are of particular interest to scientists, because they are known to explode with a standard brightness, making it possible to take accurate distance measurements for the objects.

At least, that’s true for nearby supernovae. This new survey will allow researchers to see if that pattern remains true in the distant universe too, or if they behaved differently under the conditions of the early universe. At that time, there were fewer heavy elements in the cores of stars. Finding out if this changes their behavior is essential to measuring the expansion of spacetime itself, and could help resolve the crisis in cosmology, in which measurements using type 1a supernovae don’t align with those using the Cosmic Microwave Background.

“This is really our first sample of what the high-redshift universe looks like for transient science,” said Justin Pierel, a NASA Einstein Fellow at the Space Telescope Science Institute. “We are trying to identify whether distant supernovae are fundamentally different from or very much like what we see in the nearby universe.”

Pierel carried out a preliminary examination of one of the new supernovae, found at redshift 2.9. It seems to show no difference from the expected brightness, which is good news for astronomers’ confidence in their distance measurements to date. Further analysis of other supernovae in the data will be forthcoming.

Other outcomes of this research include a better understanding of star formation and the mechanisms behind supernova explosions in the early universe.

“We’re essentially opening a new window on the transient universe,” said STScI Fellow Matthew Siebert. “Historically, whenever we’ve done that, we’ve found extremely exciting things — things that we didn’t expect.”

Learn more:

“NASA’s Webb Opens New Window on Supernova Science.” JWST.

The post Webb is an Amazing Supernova Hunter appeared first on Universe Today.

The theory of relativity predicts black holes should be able to form from light alone, but incorporating quantum effects makes it impossible

The theory of relativity predicts black holes should be able to form from light alone, but incorporating quantum effects makes it impossible

NASA’s venerable Voyager 1 spacecraft has resumed normal science operations with all four functioning instruments for the first time in more than six months

Astronomers using the CHIME telescope are looking at strange, one-off cosmic explosions with a new angle. This could bring us closer to solving the lingering mystery of fast radio bursts.

New findings show the black hole at the heart of our Milky Way galaxy had a late growth spurt.

Soil sourced directly from the lunar surface could help astronauts establish and sustain a permanent presence on the moon.

The supermassive black hole at the heart of our Milky Way Galaxy is a quiet monster. However, Sagittarius A* (or Sgr A* for short) is not totally dormant. Occasionally it gobbles down a blob of molecular gas or even a star and then suffers a bit of indigestion. That emits x-ray flares to surrounding space.

Sgr A* is the closest supermassive black hole to Earth, at a distance of 26,000 light-years. Studying the nearby environment is tough due to the black hole’s intense gravitational pull. It distorts the view of nearby objects, making them difficult to observe. However, there are ways to do it by looking at the effect of its flares on nearby molecular clouds. Astronomers recently found the centuries-old echoes of previously unknown flares that occurred long before there were telescopes to observe them. Those echoes indicate that Sgr A* eats fairly often.

Two researchers from Michigan State University—Grace Sanger-Johnson and Jack Uteg—studied the flares and their light-echoes in detail. What they found shows activity at Sgr A* in the very distant past when Sgr A* ingested material. X-ray emissions from that activity traveled for hundreds of years from Sgr A* to bounce off of and brighten a nearby molecular cloud. That created a light echo that traveled another roughly 26,000 years before reaching Earth. So, when Uteg and Sanger studied these flares and light echoes, they were literally looking into the past.

Astronomers do know about outbursts from Sgr A* from other observations. Here’s a view from NASA’s Imaging X-ray Polarimetry Explorer and Chandra X-ray Observatory. The combination of IXPE and Chandra data helped researchers determine that the X-ray light identified in the molecular clouds originated from Sagittarius A* during an outburst approximately 200 years ago. Credits: IXPE: NASA/MSFC/F. Marin et al; Chandra: NASA/CXC/SAO; Image Processing: L.Frattare, J.Major & K.Arcand Searching for Sgr A* X-ray Flares with NuSTAR

Sanger-Johnson analyzed ten years’ worth of data looking for X-ray flares generated by Sgr A*’s eating habits. During the search, she found evidence for nine more such outbursts.

The flares are typically quite dramatic. Because they’re so bright, they provide astronomers a chance to study the immediate environment around the black hole. The data Sanger-Johnson studied came from the NuSTAR mission. It zeroes in on high-energy X-ray and gamma-ray emissions. These typically come from active regions in the hearts of galaxies, supernova explosions, and other active events.

The data Sanger-Johnson collected and analyzed is now a database of flares from Sgr A. “We hope that by building up this bank of data on Sgr A flares, we and other astronomers can analyze the properties of these X-ray flares and infer the physical conditions inside the extreme environment of the supermassive black hole,” Sanger-Johnson said.

Tracking the Echoes of Flares

While Sanger-Johnson was working with the NuSTAR data, undergraduate researcher Jack Uteg studied the activity around the black hole. He analyzed 20 years of data about a giant molecular cloud called “the Bridge”. The data came from observations made by NuSTAR and the European Space Agency’s XMM-Newton observatory. The Bridge lies close to Sgr A* and normally wouldn’t give off its own light.

So, astronomers took notice when it brightened up in X-rays, according to Uteg, who is constructing a timeline of Sgr A‘s past outbursts. “The brightness we see is most likely the delayed reflection of past X-ray outbursts from Sgr A,” he said. “We first observed an increase in luminosity around 2008. Then, for the next 12 years, X-ray signals from the Bridge continued to increase until it hit peak brightness in 2020.”

Uteg’s work helped astronomers determine that Sgr A* was about five orders of magnitude brighter in X-rays than it is now. That brightening indicates our central supermassive black hole had probably cannibalized a nearby gas cloud. And, the brightness revealed other properties, according to Uteg. “One of the main reasons we care about this cloud getting brighter is that it lets us constrain how bright the Sgr A* outburst was in the past,” he said.

What Those Light-echoes from Sgr A* Reveal

Thanks to Sanger-Brown and Uteg’s work, astronomers have another way around the difficulties of observing around black holes. “Both flares and fireworks light up the darkness and help us observe things we wouldn’t normally be able to,” she said. “That’s why astronomers need to know when and where these flares occur, so they can study the black hole’s environment using that light.”

Astronomers know that the black hole does gobble up nearby material on a variable basis, but these findings help them constrain how often it happens and how the resulting flares affect the nearby neighborhood. Many questions remain about how often these flares occur and have happened in the past, according to MSU assistant professor Shuo Zhang, who acted as team lead for these two studies.

“This is the first time that we have constructed a 24-year-long variability for a molecular cloud surrounding our supermassive black hole that has reached its peak X-ray luminosity,” Zhang said. “It allows us to tell the past activity of Sgr A* from about 200 years ago. Our research team at MSU will continue this ‘astroarchaeology game’ to further unravel the mysteries of the Milky Way’s center.”

These results of the MSU team’s work were presented at the summer 2024 meeting of the American Astronomical Society.

For More Information

‘Flares’ and ‘Echoes’ from the Milky Way’s Monster Black Hole

About NuStar

About XMM-Newton

The post Echoes of Flares from the Milky Way’s Supermassive Black Hole appeared first on Universe Today.