Astronomy

A study suggests the ice giants Uranus and Neptune aren't quite as watery as previously thought. They may also contain huge amounts of frozen methane, potentially solving the puzzle of how they formed.

The unexplained mass of a remarkably massive galaxy suggests that dark matter interacts with itself, according to new observations by the James Webb Space Telescope.

The Milky Way is ancient and massive, a collection of hundreds of billions of stars, some dating back to the Universe’s early days. During its long life, it’s grown to these epic proportions through mergers with other, smaller galaxies. These mergers punctuate our galaxy’s history, and its story is written in the streams of stars left behind as evidence after a merger.

And it’s still happening today.

The Milky Way is currently digesting smaller galaxies that have come too close. The Large and Small Magellanic Clouds feel the effects as the Milky Way’s powerful gravity distorts them and siphons a stream of gas and stars from them to our galaxy. A similar thing is happening to the Sagittarius Dwarf Spheroidal Galaxy and globular clusters like Omega Centauri.

There’s a long list of these stellar streams in the Milky Way, though the original galaxies that spawned them are long gone, absorbed by the Milky Way. But the streams still tell the tale of ancient mergers and absorptions. They hold kinematic and chemical clues to the galaxies and clusters they spawned in.

As astronomers get better tools to find and study these streams, they’re realizing the streams could tell them more than just the history of mergers. They’re like strings of pearls, and their shapes and other properties show how gravity has shaped them. But they also reveal something else important: how dark matter has shaped them.

Since dark matter is so mysterious, any chance to learn something about it is a priority. As researchers examine the stellar streams, they’re finding signs of disturbances in them—including missing members—that aren’t explained by the Milky Way’s mass. They suspect that dark matter is the cause.

“If we find a pearl necklace with a few scattered pearls nearby, we can deduce that something may have come along and broken the string.”

Soon, astronomers will have an enormously powerful tool to study these streams and dark matter’s role in disturbing them: the Vera Rubin Observatory (VRO).

Astronomers have different methods of studying dark matter. Weak gravitational lensing is one of them, and it maps dark matter on the large scale of galaxy clusters. But stellar streams are at the opposite end of the scale. By mapping them and their irregularities and disturbances, astronomers can study dark matter at a much smaller scale.

This image shows the core of the Sagittarius Dwarf Spheroidal Galaxy and its stellar streams as it’s absorbed by the Milky Way. Image Credit: David Law/UCLA

The Rubin Observatory will complete its Legacy Survey of Space and Time (LSST) in a ten-year period. Alongside its time-domain astronomy objectives, the LSST will also study dark matter. The LSST Dark Energy Science Collaboration is aimed at dark matter and will use Rubin’s power to advance the study of dark energy and dark matter like nothing before it. “LSST will go much further than any of its predecessors in its ability to measure the growth of structure and will provide a stringent test of theories of modi?ed-gravity,” their website explains.

As we get closer and closer to the observatory’s planned first light in January 2025, the growing excitement is palpable.

“I’m really excited about using stellar streams to learn about dark matter,” said Nora Shipp, a postdoctoral fellow at Carnegie Mellon University and co-convener of the Dark Matter Working Group in the Rubin Observatory/LSST Dark Energy Science Collaboration. “With Rubin Observatory we’ll be able to use stellar streams to figure out how dark matter is distributed in our galaxy from the largest scales down to very small scales.”

Astronomers have ample evidence that a halo of dark matter envelops the Milky Way. Other galaxies are the same. These dark matter halos extend beyond a galaxy’s visible disk and are considered basic units in the Universe’s large-scale structure. These haloes may also contain sub-haloes, clumps of dark matter bound by gravity.

This image shows a simulated Milky Way-size CDM halo. The six circles show sub-haloes enlarged in separate boxes. Sub-haloes are also visible, and the bottom row shows several generations of sub-subhaloes contained within subhalo f. Image Credit: Zavala and Frenk 2019

These clumps are what astronomers think are leaving their marks on stellar streams. The dark matter clumps create kinks and gaps in the streams. The VRO has the power to see these irregularities on a small scale and over a ten-year span. “By observing stellar streams, we’ll be able to take indirect measurements of the Milky Way’s dark matter clumps down to masses lower than ever before, giving us really good constraints on the particle properties of dark matter,” said Shipp.

The Lambda Cold Dark Matter (Lambda CDM) model is the standard model of Big Bang Cosmology. One of the Lambda CDM’s key predictions says that many sub-galactic dark matter substructures should exist. Astronomers want to test that prediction by observing these structures’ effect on stellar streams. The VRO will help them do that and will also help them find more of them and build a larger data set.

Stellar streams are difficult to detect. Their kinematics give them away, but sometimes, there are only a few dozen stars in the streams. This obscures them among the Milky Way’s myriad stars. But the VRO will change that.

The VRO will detect streams at much further distances. On the outskirts of the Milky Way, the streams have interacted with less matter, making them strong candidates for studying the effect of dark matter in isolation.

“Stellar streams are like strings of pearls, whose stars trace the path of the system’s orbit and have a shared history,” said Jaclyn Jensen, a PhD candidate at the University of Victoria. Jensen plans to use Rubin/LSST data for her research on the progenitors of stellar streams and their role in forming the Milky Way. “Using properties of these stars, we can determine information about their origins and what kind of interactions the stream may have experienced. If we find a pearl necklace with a few scattered pearls nearby, we can deduce that something may have come along and broken the string.”

The VRO’s powerful digital camera and its system of filters make this possible. Its ultraviolet filter, in particular, will help make more streams visible. Astronomers can distinguish stellar streams from all other stars by examining the blue-ultraviolet light at the end of the visible spectrum. They’ll have thousands upon thousands of images to work with.

Rubin Observatory at twilight in May 2022. Among the observatory’s many endeavours is the study of dark matter. Credit: Rubin Obs/NSF/AURA

In fact, the VRO will unleash a deluge of astronomical data that scientists and institutions have been preparing to handle. AI and machine learning will play a foundational role in managing all that data, which should contribute to finding even more stellar streams.

“Right now it’s a labor-intensive process to pick out potential streams by eye—Rubin’s large volume of data presents an exciting opportunity to think of new, more automated ways to identify streams.”

Astronomers are still finding more stellar streams. Earlier this month, a paper in The Astrophysical Journal presented the discovery of another one. Researchers found it in Gaia’s Data Release 3. It’s likely associated with the merger of the Sequoia dwarf galaxy.

It seems certain that astronomers will keep finding more stellar streams. Their value as tracers of the Milky Way’s history is considerable. But if scientists can use them to understand the distribution of dark matter on a small scale, they’ll get more than they bargained for.

The post The Milky Way’s History is Written in Streams of Stars appeared first on Universe Today.

Boeing's Starliner spacecraft moved between buildings at NASA's Kennedy Space Center in Florida to get ready for launch. Its first astronaut mission is expected on May 6.

A team of engineers lifts the mast into place atop of NASA’s VIPER robotic Moon rover in a clean room at NASA’s Johnson Space Center in Houston.

A preview of the "Star Trek: Lower Decks" Season 4 Blu-ray and DVD, which was released today (April 16).

The robotic telescopes of the Virtual Telescope Project have observed a quasar powered by a supermassive black hole 3 billion times as massive as the sun at the very edge of the universe

Starfish feet are coordinated purely through mechanical loading, enabling the animals to bounce rhythmically along the seabed without a central nervous system

Starfish feet are coordinated purely through mechanical loading, enabling the animals to bounce rhythmically along the seabed without a central nervous system

Traditional economics makes ludicrous assumptions and poor predictions. Now an alternative approach using big data and psychological insights is proving far more accurate

Traditional economics makes ludicrous assumptions and poor predictions. Now an alternative approach using big data and psychological insights is proving far more accurate

Modelling that shows how the world can remain below 1.5°C of warming assumes we can store vast amounts of carbon dioxide underground, but a new analysis reveals that achieving this is extremely unlikely

Modelling that shows how the world can remain below 1.5°C of warming assumes we can store vast amounts of carbon dioxide underground, but a new analysis reveals that achieving this is extremely unlikely

A black hole would be tough to destroy, but in the season two premiere of Dead Planets Society our hosts are willing to go to extremes, from faster-than-light bombs to time travel

A black hole would be tough to destroy, but in the season two premiere of Dead Planets Society our hosts are willing to go to extremes, from faster-than-light bombs to time travel

BepiColombo spotted an outpour of carbon and oxygen atoms in Venus' fragile magnetic environment

Switzerland became the 37th country to sign the Artemis Accords for peaceful moon exploration with NASA on April 15, following the inclusion of Greece and Uruguay in February.

More U.S. states are requiring online ID checks. A proposed French strategy aims to balance child safety with users’ privacy rights

Hmmm spaceflight is not the easiest of enterprises. NASA have let us know that their plans for the Mars Sample Return Mission have changed. The original plan was to work with ESA to collect samples from Perseverance and return them to Earth by 2031. Alas like many things, costs were increasing and timescales were slipping and with the budget challenges, NASA has had to rework their plan. Administrator Bill Nelson has now shared a simpler, less expensive and less risk alternative.

The Mars Perseverance Rover departed Earth as part of the Mars 2020 mission on 30 July 2020. It’s no quick nip round the corner to get to the red planet so it arrived just under 7 months later on 18 February 2021. Among its many tasks was to collect rock samples, package them up into tubes and deposit them ready for collection by another future mission to return them to Earth. The samples are to be analysed in Earth based laboratories to help us understand the formation of the Solar System, to look for signs of ancient life on Mars and to enable future human exploration. So far so good but enter NASAs budgetary challenges. 

Illustration of Perseverance on Mars

In response to these budget challenges and to an independent review of the Mars Sample Return mission, NASA have had to get creative. The mission design has been updated to include a simpler, less risky approach and at lower cost. The timescales for the sample return have also now been pushed out to return the samples by 2040 instead of the original target date 9 years earlier. 

The team at NASA are under no illusions as to the complexity of the task at hand. To land safely on Mars is just the beginning. The samples have to be collected and safely stowed away, then the rocket must take off from Mars and return safely to Earth! This has never been done before without human intervention – think Apollo with astronauts bringing several kilograms of lunar samples back for analysis. 

At the time of writing this report, NASA do not yet have a way to reduce the costs yet maintain a high level of confidence of success. NASA has asked multiple teams to work together to come up with a plan that takes an innovative approach with where possible, proven technology. They are to work with other industries on proposals to find ways that the mission can be delivered to the cost challenges, with less complexity and by bringing the delivery of the samples back to the 2030’s. 

Nicky Fox, NASA’s associate administrator from Washington said “NASA does visionary science – and returning diverse, scientifically-relevant samples from Mars is a key priority.” Clearly it’s a challenge, not only the logistics of the mission itself but to bring it in given the constraints facing the team is no mean feat. One thing NASA has on its side is their can-do attitude. It’s an organisation that never fails to impress with ingenious solutions. I have no doubt that, by the end of the 2039 we will see the samples returned to Earth in another first for interplanetary exploration. 

Source : NASA Sets Path to Return Mars Samples, Seeks Innovative Designs

The post The Current Mars Sample Return Mission isn’t Going to Work. NASA is Going Back to the Drawing Board appeared first on Universe Today.