Astronomy

How does a comet tail change?

The experimental fusion reactor sustained temperatures of 180 million degrees Fahrenheit for a record-breaking 48 seconds.

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A three-legged robot named SpaceHopper could help combat challenges of exploring low-gravity environments, such as asteroids or moons.

An international research team led by the University of Vienna has made a major breakthrough. In a study recently published in Nature Astronomy, they describe how they conducted the first direct measurements of stellar wind in three Sun-like star systems. Using X-ray emission data obtained by the ESA’s X-ray Multi-Mirror-Newton (XMM-Newton) of these stars’ “astrospheres,” they measured the mass loss rate of these stars via stellar winds. The study of how stars and planets co-evolve could assist in the search for life while also helping astronomers predict the future evolution of our Solar System.

The research was led by Kristina G. Kislyakova, a Senior Scientist with the Department of Astrophysics at the University of Vienna, the deputy head of the Star and Planet Formation group, and the lead coordinator of the ERASMUS+ program. She was joined by other astrophysicists from the University of Vienna, the Laboratoire Atmosphères, Milieux, Observations Spatiales (LAMOS) at the Sorbonne University, the University of Leicester, and the Johns Hopkins University Applied Physics Laboratory (JHUAPL).

Astrospheres are the analogs of our Solar System’s heliosphere, the outermost atmospheric layer of our Sun, composed of hot plasma pushed by solar winds into the interstellar medium (ISM). These winds drive many processes that cause planetary atmospheres to be lost to space (aka. atmospheric mass loss). Assuming a planet’s atmosphere is regularly replenished and/or has a protective magnetosphere, these winds can be the deciding factor between a planet becoming habitable or a lifeless ball of rock.

Logarithmic scale of the Solar System, Heliosphere, and Interstellar Medium (ISM). Credit: NASA-JPL

While stellar winds mainly comprise protons, electrons, and alpha particles, they also contain trace amounts of heavy ions and atomic nuclei, such as carbon, nitrogen, oxygen, silicon, and even iron. Despite their importance to stellar and planetary evolution, the winds of Sun-like stars are notoriously difficult to constrain. However, these heavier ions are known to capture electrons from neutral hydrogen that permeates the ISM, resulting in X-ray emissions. Using data from the XXM-Newton mission, Kislyakova and her team detected these emissions from other stars.

These were 70 Ophiuchi, Epsilon Eridani, and 61 Cygni, three main sequence Sun-like stars located 16.6, 10.475, and 11.4 light-years from Earth (respectively). Whereas 70 Ophiuchi and 61 Cygni are binary systems of two K-type (orange dwarf) stars, Epsilon Eridani is a single K-type star. By observing the spectral lines of oxygen ions, they could directly quantify the total mass of stellar wind emitted by all three stars. For the three stars surveyed, they estimated the mass loss rates to be 66.5±11.1, 15.6±4.4, and 9.6±4.1 times the solar mass loss rate, respectively.

In short, this means that the winds from these stars are much stronger than our Sun’s, which could result from the stronger magnetic activity of these stars. As Kislyakova related in a University of Vienna news release:

“In the solar system, solar wind charge exchange emission has been observed from planets, comets, and the heliosphere and provides a natural laboratory to study the solar wind’s composition. Observing this emission from distant stars is much more tricky due to the faintness of the signal. In addition to that, the distance to the stars makes it very difficult to disentangle the signal emitted by the astrosphere from the actual X-ray emission of the star itself, part of which is “spread” over the field-of-view of the telescope due to instrumental effects.”

XMM-Newton X-ray image of the star 70 Ophiuchi (left) and the X-ray emission from the region (“Annulus”) surrounding the star represented in a spectrum over the energy of the X-ray photons (right). Credit: C: Kislyakova et al. (2024)

For their study, Kislyakova and her team also developed a new algorithm to disentangle the contributions made by the stars and their astrospheres to the emission spectra. This allowed them to detect charge exchange signals from the stellar wind oxygen ions and the neutral hydrogen in the surrounding ISM. This constitutes the first time X-ray charge exchange emissions from the extrasolar astrospheres have been directly detected. Moreover, the mass loss rate estimates they derived could be used by astronomers as a benchmark for stellar wind models, expanding on what little observational evidence there is for the winds of Sun-like stars. As co-author Manuel Güdel, also of the University of Vienna, indicated:

“There have been world-wide efforts over three decades to substantiate the presence of winds around Sun-like stars and measure their strengths, but so far only indirect evidence based on their secondary effects on the star or its environment alluded to the existence of such winds; our group previously tried to detect radio emission from the winds but could only place upper limits to the wind strengths while not detecting the winds themselves. Our new X-ray based results pave the way to finding and even imaging these winds directly and studying their interactions with surrounding planets.”

In the future, this method of direct detection of stellar winds will be facilitated by next-generation missions like the European Athena mission. This mission will include a high-resolution X-ray Integral Field Unit (X-IFU) spectrometer, which Athena will use to resolve the finer structure and ratio of faint emission lines that are difficult to distinguish using XMM-Newton’s instruments. This will provide a more detailed picture of the stellar winds and astrospheres of distant stars, helping astronomers constrain their potential habitability while also improving solar evolution models.

Further Reading: University of Vienna, Nature Astronomy

The post Stellar Winds Coming From Other Stars Measured for the First Time appeared first on Universe Today.

Will the sky be clear enough to see the eclipse?

One of the big mysteries about dark matter particles is whether they interact with each other. We still don’t know the exact nature of what dark matter is. Some models argue that dark matter only interacts gravitationally, but many more posit that dark matter particles can collide with each other, clump together, and even decay into particles we can see. If that’s the case, then objects with particularly strong gravitational fields such as black holes, neutron stars, and white dwarfs might capture and concentrate dark matter. This could in turn affect how these objects appear. As a case in point, a recent study looks at the interplay between dark matter and neutron stars.

Neutron stars are made of the most dense matter in the cosmos. Their powerful gravitational fields could trap dark matter and unlike black holes, any radiation from dark matter won’t be trapped behind an event horizon. So neutron stars are a perfect candidate for studying dark matter models. For this study, the team looked at how much dark matter a neutron star could capture, and how the decay of interacting dark matter particles would affect its temperature.

The details depend on which specific dark matter model you use. Rather than addressing variant models, the team looked at broad properties. Specifically, they focused on how dark matter and baryons (protons and neutrons) might interact, and whether that would cause dark matter to be trapped. Sure enough, for the range of possible baryon-dark matter interactions, neutron stars can capture dark matter.

The team then went on to look at how dark matter thermalization could occur. In other words, as dark matter is captured it should release heat energy into the neutron star through collisions and dark matter annihilation. Over time the dark matter and neutron star should reach a thermal equilibrium. The rate at which this occurs depends on how strongly particles interact, the so-called scattering cross-section. The team found that thermal equilibrium is reached fairly quickly. For simple scalar models of dark matter, equilibrium can be reached within 10,000 years. For vector models of dark matter, equilibrium can happen in just a year. Regardless of the model, neutron stars can reach thermal equilibrium in a cosmic blink of an eye.

If this model is correct, then dark matter could play a measurable role in the evolution of neutron stars. We could, for example, identify the presence of dark matter by observing neutron stars that are warmer than expected. Or perhaps even distinguish different dark matter models by the overall spectrum of neutron stars.

Reference: Bell, Nicole F., et al. “Thermalization and annihilation of dark matter in neutron stars.” Journal of Cosmology and Astroparticle Physics 2024.04 (2024): 006.

The post Neutron Stars Could be Heating Up From Dark Matter Annihilation appeared first on Universe Today.

On Episode 106 of This Week In Space, Rod and Tariq take you on a tour of the coolest space places on Earth.

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After a journey lasting about two billion years, photons from an extremely energetic gamma-ray burst (GRB) struck the sensors on the Neil Gehrels Swift Observatory and the Fermi Gamma-Ray Space Telescope on October 9th, 2022. The GRB lasted seven minutes but was visible for much longer. Even amateur astronomers spotted the powerful burst in visible frequencies.

It was so powerful that it affected Earth’s atmosphere, a remarkable feat for something more than two billion light-years away. It’s the brightest GRB ever observed, and since then, astrophysicists have searched for its source.

NASA says GRBs are the most powerful explosions in the Universe. They were first detected in the late 1960s by American satellites launched to keep an eye on the USSR. The Americans were concerned that the Russians might keep testing atomic weapons despite signing 1963’s Nuclear Test Ban Treaty.

Now, we detect about one GRB daily, and they’re always in distant galaxies. Astrophysicists struggled to explain them, coming up with different hypotheses. There was so much research into them that by the year 2,000, an average of 1.5 articles on GRBs were published in scientific journals daily.

There were many different proposed causes. Some thought that GRBs could be released when comets collided with neutron stars. Others thought they could come from massive stars collapsing to become black holes. In fact, scientists wondered if quasars, supernovae, pulsars, and even globular clusters could be the cause of GRBs or associated with them somehow.

GRBs are confounding because their light curves are so complex. No two are identical. But astrophysicists made progress, and they’ve learned a few things. Short-duration GRBs are caused by the merger of two neutron stars or the merger of a neutron star and a black hole. Longer-duration GRBs are caused by a massive star collapsing and forming a black hole.

This sample of 12 GRB light curves shows how no two are the same. Image Credit: NASA

New research in Nature examined the ultra-energetic GRB 221009A, dubbed the “B.O.A.T: Brightest Of All Time,” and found something surprising. When it was initially discovered, scientists said it was caused by a massive star collapsing into a black hole. The new research doesn’t contradict that. But it presents a new mystery: why are there no heavy elements in the newly uncovered supernova?

The research is “JWST detection of a supernova associated with GRB 221009A without an r-process signature.” The lead author is Peter Blanchard, a Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) postdoctoral fellow.

“The GRB was so bright that it obscured any potential supernova signature in the first weeks and months after the burst,” Blanchard said. “At these times, the so-called afterglow of the GRB was like the headlights of a car coming straight at you, preventing you from seeing the car itself. So, we had to wait for it to fade significantly to give us a chance of seeing the supernova.”

“When we confirmed that the GRB was generated by the collapse of a massive star, that gave us the opportunity to test a hypothesis for how some of the heaviest elements in the universe are formed,” said lead author Blanchard. “We did not see signatures of these heavy elements, suggesting that extremely energetic GRBs like the B.O.A.T. do not produce these elements. That doesn’t mean that all GRBs do not produce them, but it’s a key piece of information as we continue to understand where these heavy elements come from. Future observations with JWST will determine if the B.O.A.T.’s ‘normal’ cousins produce these elements.”

Scientists know that supernova explosions forge heavy elements. They’re an important source of elements from oxygen (atomic number 8) to rubidium (atomic number 37) in the interstellar medium. They also produce heavier elements than that. Heavy elements are necessary to form rocky planets like Earth and for life itself. But it’s important to note that astrophysicists don’t completely understand how heavy elements are produced.

This periodic table from the NASA Scientific Visualization Studio shows where the elements come from, though scientists still have some uncertainty. Image Credit: NASA’s Goddard Space Flight Center

Scientists naturally wondered if an extremely luminous GRB like GRB 221009A would produce even more heavy elements. But that’s not what they found.

“This event is particularly exciting because some had hypothesized that a luminous gamma-ray burst like the B.O.A.T. could make a lot of heavy elements like gold and platinum,” said second author Ashley Villar of Harvard University and the Center for Astrophysics | Harvard & Smithsonian. “If they were correct, the B.O.A.T. should have been a goldmine. It is really striking that we didn’t see any evidence for these heavy elements.”

Stars forge heavy elements by nucleosynthesis. Three processes are responsible for that: the p-process, the s-process and the r-process (proton capture process, slow neutron capture process, and the rapid neutron capture process.) The r-process captures neutrons faster than the s-process and is responsible for about half of the elements heavier than iron. The r-process is also responsible for the most stable isotopes of these heavy elements.

That’s all to illustrate the importance of the r-process in the Universe.

The researchers used the JWST to get to the bottom of GRB 221009A. The GRB was obscured by the Milky Way, but the JWST senses infrared light and saw right through the Milky Way’s gas and dust. The telescope’s NIRSpec (Near Infrared Spectrograph) senses elements like oxygen and calcium, usually found in supernovae. But the signatures weren’t very bright, a surprise considering how bright the supernova was.

“It’s not any brighter than previous supernovae,” lead author Blanchard said. “It looks fairly normal in the context of other supernovae associated with less energetic GRBs. You might expect that the same collapsing star producing a very energetic and bright GRB would also produce a very energetic and bright supernova. But it turns out that’s not the case. We have this extremely luminous GRB, but a normal supernova.”

Confirming the presence of the supernova was a big step to understanding GRB 221009A. But the lack of an r-process signature is still confounding.

Scientists have only confirmed the r-process in the merger of two neutron stars, called a kilonova explosion. But there are too few neutron star mergers to explain the abundance of heavy elements.

This artist’s illustration shows two neutron stars colliding. Known as a “kilonova” event, they’re the only confirmed location of the r-process that forges heavy elements. Credits: Elizabeth Wheatley (STScI)

“There is likely another source,” Blanchard said. “It takes a very long time for binary neutron stars to merge. Two stars in a binary system first have to explode to leave behind neutron stars. Then, it can take billions and billions of years for the two neutron stars to slowly get closer and closer and finally merge. But observations of very old stars indicate that parts of the universe were enriched with heavy metals before most binary neutron stars would have had time to merge. That’s pointing us to an alternative channel.”

Researchers have wondered if luminous supernovae like this can account for the rest. Supernovae have an inner layer where more heavy elements could be synthesized. But that layer is obscured. Only after things calm down is the inner layer visible.

“The exploded material of the star is opaque at early times, so you can only see the outer layers,” Blanchard said. “But once it expands and cools, it becomes transparent. Then you can see the photons coming from the inner layer of the supernova.”

All elements have spectroscopic signatures, and the JWST’s NIRSpec is a very capable instrument. But it couldn’t detect heavier elements, even in the supernova’s inner layer.

“Upon examining the B.O.A.T.’s spectrum, we did not see any signature of heavy elements, suggesting extreme events like GRB 221009A are not primary sources,” lead author Blanshard said. “This is crucial information as we continue to try to pin down where the heaviest elements are formed.”

Scientists are still uncertain about the GRB and its lack of heavy elements. But there’s another feature that might offer a clue: jets.

“A second proposed site of the r-process is in rapidly rotating cores of massive stars that collapse into an accreting black hole, producing similar conditions as the aftermath of a BNS merger,” the authors write in their paper. “Theoretical simulations suggest that accretion disk outflows in these so-called ‘collapsars’ may reach the neutron-rich state required for the r-process to occur.”

The “accretion disk outflows” the researchers refer to are relativistic jets. The narrower the jets are, the brighter and more focused their energy is.

Could they play a role in forging heavy elements?

“It’s like focusing a flashlight’s beam into a narrow column, as opposed to a broad beam that washes across a whole wall,” Laskar said. “In fact, this was one of the narrowest jets seen for a gamma-ray burst so far, which gives us a hint as to why the afterglow appeared as bright as it did. There may be other factors responsible as well, a question that researchers will be studying for years to come.”

The researchers also used NIRSpec to gather a spectrum from the GRB’s host galaxy. It has the lowest metallicity of any galaxy known to host a GRB. Could that be a factor?

“This is one of the lowest metallicity environments of any LGRB, which is a class of objects that prefer low-metallicity galaxies, and it is, to our knowledge, the lowest metallicity environment of a GRB-SN to date,” the authors write in their research. “This may suggest that very low metallicity is required to produce a very energetic GRB.”

The host galaxy is also actively forming stars. Is that another clue?

“The spectrum shows signs of star formation, hinting that the birth environment of the original star may be different than previous events,” Blanshard said.

Yijia Li is a graduate student at Penn State and a co-author of the paper. “This is another unique aspect of the B.O.A.T. that may help explain its properties,” Li said. “The energy released in the B.O.A.T. was completely off the charts, one of the most energetic events humans have ever seen. The fact that it also appears to be born out of near-primordial gas may be an important clue to understanding its superlative properties.”

This is another case where solving one mystery leads to another unanswered one. The JWST was launched to answer some of our foundational questions about the Universe. By confirming that a supernova is behind the most powerful GRB ever detected, it’s done part of its job.

But it also found another mystery and has left us hanging again.

The JWST is working as intended.

The post The Brightest Gamma Ray Burst Ever Seen Came from a Collapsing Star appeared first on Universe Today.

It’s an exciting time for the fields of astronomy, astrophysics, and cosmology. Thanks to cutting-edge observatories, instruments, and new techniques, scientists are getting closer to experimentally verifying theories that remain largely untested. These theories address some of the most pressing questions scientists have about the Universe and the physical laws governing it – like the nature of gravity, Dark Matter, and Dark Energy. For decades, scientists have postulated that either there is additional physics at work or that our predominant cosmological model needs to be revised.

While the investigation into the existence and nature of Dark Matter and Dark Energy is ongoing, there are also attempts to resolve these mysteries with the possible existence of new physics. In a recent paper, a team of NASA researchers proposed how spacecraft could search for evidence of additional physical within our Solar Systems. This search, they argue, would be assisted by the spacecraft flying in a tetrahedral formation and using interferometers. Such a mission could help resolve a cosmological mystery that has eluded scientists for over half a century.

The proposal is the work of Slava G. Turyshev, an adjunct professor of physics and astronomy at the University of California Los Angeles (UCLA) and research scientist with NASA’s Jet Propulsion Laboratory. He was joined by Sheng-wey Chiow, an experimental physicist at NASA JPL, and Nan Yu, an adjunct professor at the University of South Carolina and a senior research scientist at NASA JPL. Their research paper recently appeared online and has been accepted for publication in Physical Review D.

A new study shows how measuring the Sun’s gravitational field could search for additional physics. Credit: NASA/ESA

Turyshev’s experience includes being a Gravity Recovery And Interior Laboratory (GRAIL) mission science team member. In previous work, Turyshev and his colleagues have investigated how a mission to the Sun’s solar gravitational lens (SGL) could revolutionize astronomy. The concept paper was awarded a Phase III grant in 2020 by NASA’s Innovative Advanced Concepts (NIAC) program. In a previous study, he and SETI astronomer Claudio Maccone also considered how advanced civilizations could use SGLs to transmit power from one solar system to the next.

To summarize, gravitational lensing is a phenomenon where gravitational fields alter the curvature of spacetime in their vicinity. This effect was originally predicted by Einstein in 1916 and was used by Arthur Eddington in 1919 to confirm his General Relativity (GR). However, between the 1960s and 1990s, observations of the rotational curves of galaxies and the expansion of the Universe gave rise to new theories regarding the nature of gravity over larger cosmic scales. On the one hand, scientists postulated the existence of Dark Matter and Dark Energy to reconcile their observations with GR.

On the other hand, scientists have advanced alternate theories of gravity (such as Modified Newtonian Dynamics (MOND), Modified Gravity (MOG), etc.). Meanwhile, others have suggested there may be additional physics in the cosmos that we are not yet aware of. As Turyshev told Universe Today via email:

“We are eager to explore questions surrounding the mysteries of dark energy and dark matter. Despite their discovery in the last century, their underlying causes remain elusive. Should these ‘anomalies’ stem from new physics—phenomena yet to be observed in ground-based laboratories or particle accelerators—it’s possible that this novel force could manifest on a solar system scale.”

Artist’s impression of a proposed Solar Gravity Lens telescope. Credit: The Aerospace Corporation

For their latest study, Turyshev and his colleagues investigated how a series of spacecraft flying in a tetrahedral formation could investigate the Sun’s gravitational field. These investigations, said Turyshev, would search for deviations from the predictions of general relativity at the Solar System scale, something that has not been possible to date:

“These deviations are hypothesized to manifest as nonzero elements in the gravity gradient tensor (GGT), fundamentally akin to a solution of the Poisson equation. Due to their minuscule nature, detecting these deviations demands precision far surpassing current capabilities—by at least five orders of magnitude. At such a heightened level of accuracy, numerous well-known effects will introduce significant noise. The strategy involves conducting differential measurements to negate the impact of known forces, thereby revealing the subtle, yet nonzero, contributions to the GGT.”

The mission, said Turyshev, would employ local measurement techniques that rely on a series of interferometers. This includes interferometric laser ranging, a technique demonstrated by the Gravity Recovery and Climate Experiment Follow-On (GRACE-FO) mission, a spacecraft pair that relies on laser range finding to track Earth’s oceans, glaciers, rivers, and surface water. The same technique will also be used to investigate gravitational waves by the proposed space-based Laser Interferometry Space Antenna (LISA).

The spacecraft will also be equipped with atom interferometers, which use the wave character of atoms to measure the difference in phase between atomic matter waves along different paths. This technique will allow the spacecraft to detect the presence of non-gravitational noise (thruster activity, solar radiation pressure, thermal recoil forces, etc.) and negate them to the necessary degree. Meanwhile, flying in a tetrahedral formation will optimize the spacecraft’s ability to compare measurements.

“Laser ranging will offer us highly accurate data on the distances and relative velocities between spacecraft,” said Turyshev. “Furthermore, its exceptional precision will allow us to measure the rotation of a tetrahedron formation relative to an inertial reference frame (via Sagnac observables), a task unachievable by any other means. Consequently, this will establish a tetrahedral formation leveraging a suite of local measurements.”

Artist’s impression of the path of the star S2 as it passes very close to the supermassive black hole at the center of the Milky Way. Credit: ESO/M. Kornmesser

Ultimately, this mission will test GR on the smallest of scales, which has been sorely lacking to date. While scientists continue to probe the effect of gravitational fields on spacetime, these have been largely confined to using galaxies and galaxy clusters as lenses. Other instances include observations of compact objects (like white dwarf stars) and supermassive black holes (SMBH) like Sagittarius A* – which resides at the center of the Milky Way.

“We aim to enhance the precision of testing GR and alternative gravitational theories by more than five orders of magnitude. Beyond this primary objective, our mission has additional scientific goals, which we will detail in our subsequent paper. These include testing GR and other gravitational theories, detecting gravitational waves in the micro-Hertz range—a spectrum not reachable by existing or envisioned instruments— and exploring aspects of the solar system, such as the hypothetical Planet 9, among other endeavors.”

Further Reading: Physical Review D

The post Formation-Flying Spacecraft Could Probe the Solar System for New Physics appeared first on Universe Today.

Vulcan, United Launch Alliance's new heavy-lift rocket, was not the result of being exposed to gamma rays or the bite of a radioactive spider, but it does have an origin story worthy of a comic book.

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