In the constellation of Orion, there is a brilliant bluish-white star. It marks the right foot of the starry hunter. It’s known as Rigel, and it is the most famous example of a blue supergiant star. Blue supergiants are more than 10,000 times brighter than the Sun, with masses 16 – 40 times greater. They are unstable and short-lived, so they should be rare in the galaxy. While they are rare, blue supergiants aren’t as rare as we would expect. A new study may have figured out why.
We aren’t entirely sure how these massive stars form, though one idea is that they occur when a massive main sequence star passes through an interstellar cloud. By capturing gas and dust from the cloud, a star can shift off the main sequence to become a blue supergiant. Another idea is that they may form within stellar nurseries with a mass as great as 300 Suns. As a result, they quickly burn so brightly that they never become true main-sequence stars. Both of these models predict that blue supergiants are much more rare than the number we observe.
This new study starts by noting that blue supergiants, particularly the smaller ones known as B-type supergiants, are rarely seen with companion stars. This is odd since most massive stars form as part of a binary or multiple system. The authors propose that B-type blue supergiants aren’t often in binary systems because they typically are the product of binary mergers.
The team simulated a range of models where a giant main-sequence star has a smaller close-orbiting companion and then looked at what would result if the two stars merged. They then compared the results to observations of 59 young blue supergiant stars in the Large Magellanic Cloud. They found that not only can these mergers produce blue supergiants in the mass range of the Magellanic stars, but the spectra of the simulated mergers match the spectra of the 59 blue supergiants. This strongly suggests that many if not most B-type blue supergiants are the result of stellar mergers.
In the future, the team would like to carry this work further to see how blue supergiants evolve into neutron stars and black holes. This could help explain the type of mergers observed by gravitational wave observatories such as LIGO and Virgo.
Reference: Menon, Athira, et al. “Evidence for Evolved Stellar Binary Mergers in Observed B-type Blue Supergiants.” The Astrophysical Journal Letters 963.2 (2024): L42.
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Using ESA’s Gaia spacecraft, astronomers have tracked down two streams of stars that likely formed the foundation of the Milky Way. Named “Shakti and Shiva,” the two streams contain about 10 million stars, all of which are 12 to 13 billion years old and likely came together even before the spiral arms and disk were formed. These star streams are all moving in roughly similar orbits and have similar compositions. Astronomers think they were probably separate galaxies that merged into the Milky Way shortly after the Big Bang.,
“What’s truly amazing is that we can detect these ancient structures at all,” said lead author Khyati Malhan of the Max Planck Institute for Astronomy (MPIA) in Heidelberg, Germany, in an ESA press release. “The Milky Way has changed so significantly since these stars were born that we wouldn’t expect to recognize them so clearly as a group – but the unprecedented data we’re getting from Gaia made it possible.”
Astrometry DataGaia uses astrometry — the precise measurements of the positions and movements of stars and other celestial bodies – and is building the largest, most precise three-dimensional map of our Galaxy by surveying nearly two billion objects.
With Gaia’s data, the researchers were able to determine the orbits of individual stars in the Milky Way, as well as determine their content and composition. These ancient stars are all moving in very similar orbits and the structure of the two different star streams stood out because their stars contained a certain chemical composition.
“Shakti and Shiva populations possess an unconventional combination of orbital and abundance properties that have not been observed previously,” the researchers wrote in their paper, published in the Astrophysical journal.
By compiling very detailed chemical abundance patterns for each, the astronomers determined these stars were the oldest stars in the galaxy, all born before the disc of the Milky Way had formed.
The components of the Milky Way Galaxy. This artist’s impression shows our roughly 13 billon-year-old ‘barred spiral galaxy’ that is home to a few hundred billion stars. Credit: Left: NASA/JPL-Caltech; right: ESA; layout: ESA/ATG medialab.“The stars there are so ancient that they lack many of the heavier metal elements created later in the Universe’s lifetime,” said co-author Hans-Walter Rix, also of MPIA and the lead ‘galactic archaeologist’ in this research, which began in 2022. “These heavy metals are those forged within stars and scattered through space when they die. The stars in our galaxy’s heart are metal-poor, so we dubbed this region the Milky Way’s ‘poor old heart’. Until now, we had only recognized these very early fragments that came together to form the Milky Way’s ancient heart. With Shakti and Shiva, we now see the first pieces that seem comparably old but located further out. These signify the first steps of our galaxy’s growth towards its present size.”
While the two streams are similar, they aren’t exactly the same. Shakti stars orbit a little further from the Milky Way’s center and in more circular orbits than Shiva stars. The streams are named two divine beings from Hindu philosophy who worked together to create the Universe.
Because of Gaia’s ability to provide data to create incredibly detailed celestial maps, the researchers were able to build a dynamical map of that includes the two star streams plus other known components that have played a role in our galaxy’s formation.
“Revealing more about our galaxy’s infancy is one of Gaia’s goals, and it’s certainly achieving it,” said Timo Prusti, Project Scientist for Gaia at ESA. “We need to pinpoint the subtle yet crucial differences between stars in the Milky Way to understand how our galaxy formed and evolved. This requires incredibly precise data – and now, thanks to Gaia, we have that data. As we discover surprise parts of our galaxy like the Shiva and Shakti streams, we’re filling the gaps and painting a fuller picture of not only our current home, but our earliest cosmic history.”
Further reading:
ESA press release
Paper: Shiva and Shakti: Presumed Proto-Galactic Fragments in the Inner Milky Way
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In a win for planetary scientists, and planetary geologists in particular, it was announced at the recent 55th Lunar and Planetary Science Conference (LPSC) in Texas earlier this month that NASA’s VERITAS mission to the planet Venus has been reinstated into NASA’s Fiscal Year 2025 (FY25) budget with a scheduled launch date of 2031, with the unofficial announcement coming on the first day of the conference, March 11, 2024, and being officially announced just a few days later. This comes after VERITAS experienced a “soft cancellation” in March of last year when NASA revealed its FY24 budget, providing VERITAS only $1.5 million, which was preceded by the launch of VERITAS being delayed a minimum of three years due to findings from an independent review board in November 2022.
VERITAS is back in the budget!! ??? The project will get going full swing this fall (FY25). We’re looking at a 31 launch (TBC). Thanks to everyone who’s supported our return to Venus!! It’s going to be fabulous ?
— Sue Smrekar (@SueSmrekar) March 11, 2024 Dr. Sue Smrekar, who is the Principal Investigator for the VERITAS mission, announcing during LPSC 2024 that VERITAS has been reinstated.Here, Universe Today speaks with Dr. Paul Byrne, who is an Associate Professor of Earth, Environmental, and Planetary Sciences at Washington University in St. Louis, and a huge proponent of exploring Venus, about his thoughts on VERITAS being reinstated, the alleged events that led to VERITAS’ reinstatement, his experience between VERITAS being postponed to now, and his thoughts on what science VERITAS hopes to accomplish at Venus. So, what are his thoughts on VERITAS being reinstated?
“First and foremost, it’s relief,” Dr. Byrne tells Universe Today. “Although VERITAS wasn’t cancelled per se, we in the planetary community weren’t sure if or where VERITAS would be reinstated. Although it’s disappointing to have a selected mission be delayed, it’s a very positive sign that VERITAS is back in the budget. Of course, there’s a flip side to this development: the mission’s stablemate, DAVINCI, has itself been delayed. It’s clear that the prevailing budget situation at NASA is very tough right now, and lots of missions are feeling it. Unfortunately, with two Venus missions in the pipeline, the Venus community is feeling this budget toughness most acutely.”
After years of being proposed as a NASA Discovery mission, VERITAS was officially selected in June 2021, along with DAVINCI (previously known as DAVINCI+) to explore the second planet from the Sun like never before. While VERITAS will be tasked with producing new surface maps of Venus, DAVINCI was tasked with conducting atmospheric science, as debate continues over the potential habitability of Venus’ atmosphere. With an initial scheduled launch date between 2028 and 2030, the November 2022 findings pushed this back to 2031, only to result in the “soft cancellation” just months later. With the planetary science community pushing for VERITAS to be reinstated over the last 12 months, what led to VERITAS being reinstated?
“A major part of it was, in my view, strong advocacy not only by the Venus community but by the planetary science community at large,” Dr. Byrne tells Universe Today. “Other advisory groups—volunteer groups charged with collating and representing to NASA the needs of a given portion of the planetary science community—voiced very loud, strong support for VERITAS beyond just the Venus community, in a wonderful example of community-wide support. Groups such as The Planetary Society also lent their voice to supporting VERITAS. That advocacy was noticed by NASA HQ and by Congress, which played no small role in getting VERITAS back into the budget.”
While not officially a member of the VERITAS mission team, Dr. Byrne has a myriad of publications about Venus, including as a co-author on five LPSC 2024 studies that discussed lava flow cooling, Venus’ potential habitability as an analog for other planets, predicting tectonic activity, predicting future volcanic activity, and current active volcanism. Additionally, Dr. Byrne has expressed his continued support via social media for both the second planet from the Sun and the VERITAS and DAVINCI missions throughout their respective journeys, and specifically when they were selected in June 2021. Therefore, what kind of emotional roller coaster has he experienced between VERITAS being canceled and now?
“It’s so hard to see a mission being selected for a science target NASA hasn’t been to in forty years, only for it to be postponed through no fault of the mission team itself,” Dr. Byrne tells Universe Today. “And it’s wonderful that we now know VERITAS will fly, even if it’s later than originally planned. But I’m keenly aware, as someone who’s not a member of the VERITAS team, that the highs and lows I’ve experienced are nothing compared with those of the team itself, who put their heart and soul (and at least three attempts!) to get VERITAS selected. Better late than never, but better on time than late. Still, we make do with the circumstances we face!”
As Dr. Byrne alluded to, the last NASA mission to Venus was the Magellan spacecraft, which was launched on May 4, 1989, from the Space Shuttle Atlantis during the STS-30R mission and arrived at Venus on August 10, 1990. Over the course of the next four years, Magellan used its synthetic aperture radar to map the entire surface of Venus since the extreme thickness of Venus’ clouds prevents direct imaging of the surface.
After Magellan’s first imaging cycle that lasted 243 days, it successfully mapped 83.7 percent of Venus’ surface, which increased to 96 percent after its second cycle and completed its mission at 98 percent after its third cycle. As a result, Magellan images identified a myriad of features across the Venusian surface, including volcanic evidence, tectonic activity, lava channels, pancake-shaped domes, and stormy winds across the surface. Therefore, with VERIATS equally tasked with mapping Venus’ surface, what science does VERITAS hope to achieve at Venus?
“VERITAS will carry a radar to Venus to obtain the most comprehensive, accurate, and highest-resolution radar image and topographic data ever acquired for the second planet,” Dr. Byrne tells Universe Today. “VERITAS will also be able to acquire spectral measurements of the surface in the infrared, offering us new insight into the composition of the planet’s surface materials. Moreover, the topographic and geodetic data VERITAS will return will in turn be used to help calibrate data from DAVINCI and the ESA EnVision mission, too.”
What new discoveries will VERITAS make about Venus in the coming years and decades? Only time will tell, and this is why we science!
As always, keep doing science & keep looking up!
The post NASA’s VERITAS Mission Breathes New Life appeared first on Universe Today.
If we could detect a clear, unambiguous biosignature on just one of the thousands of exoplanets we know of, it would be a huge, game-changing moment for humanity. But it’s extremely difficult. We simply aren’t in a place where we can be certain that what we’re detecting means what we think or even hope it does.
But what if we looked at many potential worlds at once?
It’s assumptions that plague us. Every chemical we detect in an exoplanet atmosphere, even with the powerful JWST, is accompanied by a set of assumptions. We simply don’t know enough yet for it to be any other way. This puts us in a difficult place, considering the magnitude of the question we’re trying to answer: is there life beyond Earth?
“A fundamental goal of astrobiology is to detect life outside of Earth,” write the authors of a new paper. It’s titled “An Agnostic Biosignature Based on Modeling Panspermia and Terraformation,” and it’s available on the pre-press site arxiv.org. The authors are Harrison B. Smith and Lana Sinapayen. Smith is from the Earth-Life Science Institute at the Tokyo Institute of Technology in Japan, and Sinapayen is from the Sony Computer Science Laboratories in Kyoto, Japan.
The fundamental goal that the pair of authors give voice to is a difficult one to reach. “This proves to be an exceptional challenge outside of our solar system, where strong assumptions must be made about how life would manifest and interact with its planet,” the authors explain. We only know how Earth’s biosphere works, and we’re left to assume what similarities there might be with other planets. We don’t have any consensus about how biospheres might be able to work. We’re not completely ignorant, as chemistry and physics make some things possible and others impossible. But we’re not an authority on biospheres.
Scientists are pretty good at modelling things and trying to generate useful answers, as well as generating relevant questions they might not have thought of without models. In this work, the pair of authors took a different approach to understanding life on other worlds and what effort we can make to detect it.
“Here we explore a model of life spreading between planetary systems via panspermia and terraformation,” the authors write. “Our model shows that as life propagates across the galaxy, correlations emerge between planetary characteristics and location and can function as a population-scale agnostic biosignature.”
The word ‘agnostic’ is key here. It means that they’re aiming to detect a biosignature that’s independent of the assumptions we’re normally saddled with. “This biosignature is agnostic because it is independent of strong assumptions about any particular instantiation of life or planetary characteristic—by focusing on a specific hypothesis of what life may do rather than what life may be,” the authors explain.
This approach is different. They analyze planets by their observed characteristics and then cluster them based on those observations. Then, they examine the spatial extent of the clusters themselves. That leads to a way to prioritize individual planets for their potential to harbour life.
Panspermia and terraforming play key roles. We know that rocks can travel between worlds, and that’s called lithopanspermia. Powerful impacts on Mars lofted rocks into space, some of which eventually fell to Earth. If dormant organisms like spores could survive the journey, it’s at least feasible that life could spread this way.
Panspermia is the idea that life is spread throughout the galaxy, or even the Universe, by asteroids, comets, and even minor planets. Credit: NASA/Jenny MottorTerraforming is self-explanatory for the most part. It’s the effort to engineer a world to be more habitable. If there are other technological, space-faring civilizations out there, one useful working assumption is that they’ll eventually terraform other worlds if they last long enough. In any case, even non-technological life can purposefully alter its environment. (Sit and watch beavers sometime.)
The authors make an interesting point regarding panspermia and terraforming. They’re both things that life already does, kind of. “Ultimately, our postulates of panspermia and terraformation are merely well-understood hallmarks of life (proliferation via replication and adaptation with bi-directional environmental feedback), escalated to the planetary scale, and executed on an interstellar scale,” they write.
The authors’ model shows that the way planets are distributed around stars, along with their other characteristics, could be evidence of life without even attempting to detect chemical biosignatures. This is the agnostic part of their work. It’s more powerful than a one-planet-at-a-time struggle to detect biosignatures, as plagued as that effort is by assumptions. Single planets with detected biosignatures can always be explained away by something anomalous. But that’s harder to do in this agnostic method.
“Hypothesizing that life spreads via panspermia and terraformation allows us to search for biosignatures while forgoing any strong assumptions about not only the peculiarities of life (e.g., its metabolism) and planetary habitability (e.g., requiring surface liquid water) but even the potential breadth of structure and chemical complexity underpinning living systems,” the authors explain.
This figure from the study helps illustrate the authors’ work. A shows a target planet selection, where an initial planet and its composition are randomly selected. This planet represents a terraformed parent planet. B shows the simulation run beginning with the initial parent planet, showing how nearby planets will be terraformed to more closely match the parent planet. C shows how each terraformed planet will retain some of its differences, about 10% in the researchers’ model. Image Credit: Smith and Sinapayen, 2024.We’re accustomed to thinking about specific chemicals, and the types of atmospheres exoplanets have to determine the presence of biosignatures. But that’s not how this works. This model is agnostic, so it’s not really about specific chemical biosignatures. It’s more about the patterns and clusters we could detect in populations of planets that could signal the presence of life via panspermia and terraforming.
Terraformed planets can be identified from their clustering, the authors claim. That’s because when they’re terraformed, the planets need to reflect the originating planet.
This figure from the research shows how simulated terraformed planets would appear clustered on a graph. This is a projection of 3D planet locations in the 2D X-Y plane and the earliest time step where the researchers detect a cluster of planets meeting their selection criteria. True terraformed planets have a blue fill, while planets detected by their selection method have a red outline. Image Credit: Smith and Sinapayen, 2024.There are obstacles to this method that limit its usefulness and implementation. According to the authors, they need to identify “… specific ways in which better understanding astrophysical and planetary processes would improve our ability to detect life,” the authors write.
But even without more specifics, the method is thought-provoking and creative. In the end, the authors’ model and method lead to a novel way to think about life’s hierarchies and how these hierarchies might be replicated on other planets.
If this method is strengthened and more fully developed, who knows what it might lead to?
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