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Hubble Finds Surprises Around a Star That Erupted 40 Years Ago
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Hubble Finds Surprises Around a Star That Erupted 40 Years Ago This artist’s concept shows the nova system HM Sagittae (HM Sge), where a white dwarf star is pulling material from its red giant companion. This forms a blazing hot disk around the dwarf, which can unpredictably undergo a spontaneous thermonuclear explosion as the infall of hydrogen from the red giant grows denser and reaches a tipping point. These fireworks between companion stars are fascinating to astronomers by yielding insights into the physics and dynamics of stellar evolution in binary systems. NASA, ESA, Leah Hustak (STScI)
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Astronomers have used new data from NASA’s Hubble Space Telescope and the retired SOFIA (Stratospheric Observatory for Infrared Astronomy) as well as archival data from other missions to revisit one of the strangest binary star systems in our galaxy – 40 years after it burst onto the scene as a bright and long-lived nova. A nova is a star that suddenly increases its brightness tremendously and then fades away to its former obscurity, usually in a few months or years.
Between April and September 1975, the binary system HM Sagittae (HM Sge) grew 250 times brighter. Even more unusual, it did not rapidly fade away as novae commonly do, but has maintained its luminosity for decades. Recently, observations show that the system has gotten hotter, but paradoxically faded a little.
HM Sge is a particular kind of symbiotic star where a white dwarf and a bloated, dust-producing giant companion star are in an eccentric orbit around each other, and the white dwarf ingests gas flowing from the giant star. That gas forms a blazing hot disk around the white dwarf, which can unpredictably undergo a spontaneous thermonuclear explosion as the infall of hydrogen from the giant grows denser on the surface until it reaches a tipping point. These fireworks between companion stars fascinate astronomers by yielding insights into the physics and dynamics of stellar evolution in binary systems.
When I first saw the new data, I went – ‘wow this is what Hubble UV spectroscopy can do!’ – I mean it’s spectacular, really spectacular.Ravi Sankrit
Astronomer
“In 1975 HM Sge went from being a nondescript star to something all astronomers in the field were looking at, and at some point that flurry of activity slowed down,” said Ravi Sankrit of the Space Telescope Science Institute (STScI) in Baltimore. In 2021, Steven Goldman of STScI, Sankrit and collaborators used instruments on Hubble and SOFIA to see what had changed with HM Sge in the last 30 years at wavelengths of light from the infrared to the ultraviolet (UV).
The 2021 ultraviolet data from Hubble showed a strong emission line of highly ionized magnesium that was not present in earlier published spectra from 1990. Its presence shows that the estimated temperature of the white dwarf and accretion disk increased from less than 400,000 degrees Fahrenheit in 1989 to greater than 450,000 degrees Fahrenheit now. The highly ionized magnesium line is one of many seen in the UV spectrum, which analyzed together will reveal the energetics of the system, and how it has changed in the last three decades.
“When I first saw the new data,” Sankrit said, “I went – ‘wow this is what Hubble UV spectroscopy can do!’ – I mean it’s spectacular, really spectacular.”
A Hubble Space Telescope image of the symbiotic star Mira HM Sge. Located 3,400 light-years away in the constellation Sagitta, it consists of a red giant and a white dwarf companion. The stars are too close together to be resolved by Hubble. Material bleeds off the red giant and falls onto the dwarf, making it extremely bright. This system first flared up as a nova in 1975. The red nebulosity is evidence of the stellar wind. The nebula is about one-quarter light-year across. NASA, ESA, Ravi Sankrit (STScI), Steven Goldman (STScI); Image Processing: Joseph DePasquale (STScI)
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With data from NASA’s flying telescope SOFIA, which retired in 2022, the team was able to detect the water, gas, and dust flowing in and around the system. Infrared spectral data shows that the giant star, which produces copious amounts of dust, returned to its normal behavior within only a couple years of the explosion, but also that it has dimmed in recent years, which is another puzzle to be explained.
With SOFIA astronomers were able to see water moving at around 18 miles per second, which they suspect is the speed of the sizzling accretion disk around the white dwarf. The bridge of gas connecting the giant star to the white dwarf must presently span about 2 billion miles.
The team has also been working with the AAVSO (American Association of Variable Star Observers), to collaborate with amateur astronomers from around the world who help keep telescopic eyes on HM Sge; their continued monitoring reveals changes that haven’t been seen since its outburst 40 years ago.
“Symbiotic stars like HM Sge are rare in our galaxy, and witnessing a nova-like explosion is even rarer. This unique event is a treasure for astrophysicists spanning decades,” said Goldman.
The initial results from the team’s research were published in the Astrophysical Journal, and Sankrit is presenting research focused on the UV spectroscopy at the 244th meeting of the American Astronomical Society in Madison, Wisconsin.
The Hubble Space Telescope has been operating for over three decades and continues to make ground-breaking discoveries that shape our fundamental understanding of the universe. Hubble is a project of international cooperation between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope and mission operations. Lockheed Martin Space, based in Denver, Colorado, also supports mission operations at Goddard. The Space Telescope Science Institute in Baltimore, Maryland, which is operated by the Association of Universities for Research in Astronomy, conducts Hubble science operations for NASA.
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Claire Andreoli
NASA’s Goddard Space Flight Center, Greenbelt, MD
claire.andreoli@nasa.gov
Ray Villard
Space Telescope Science Institute, Baltimore, MD
Science Contacts:
Ravi Sankrit
Space Telescope Science Institute, Baltimore, MD
Steven Goldman
Space Telescope Science Institute, Baltimore, MD
Since its 1990 launch, the Hubble Space Telescope has changed our fundamental understanding of the universe.
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NASA’s Webb Opens New Window on Supernova Science
Peering deeply into the cosmos, NASA’s James Webb Space Telescope is giving scientists their first detailed glimpse of supernovae from a time when our universe was just a small fraction of its current age. A team using Webb data has identified 10 times more supernovae in the early universe than were previously known. A few of the newfound exploding stars are the most distant examples of their type, including those used to measure the universe’s expansion rate.
“Webb is a supernova discovery machine,” said Christa DeCoursey, a third-year graduate student at the Steward Observatory and the University of Arizona in Tucson. “The sheer number of detections plus the great distances to these supernovae are the two most exciting outcomes from our survey.”
DeCoursey presented these findings in a press conference at the 244th meeting of the American Astronomical Society in Madison, Wisconsin.
Image A: Jades Deep Field Annotated The JADES Deep Field uses observations taken by NASA’s James Webb Space Telescope (JWST) as part of the JADES (JWST Advanced Deep Extragalactic Survey) program. A team of astronomers studying JADES data identified about 80 objects (circled in green) that changed in brightness over time. Most of these objects, known as transients, are the result of exploding stars or supernovae.
Prior to this survey, only a handful of supernovae had been found above a redshift of 2, which corresponds to when the universe was only 3.3 billion years old — just 25% of its current age. The JADES sample contains many supernovae that exploded even further in the past, when the universe was less than 2 billion years old. It includes the farthest one ever spectroscopically confirmed, at a redshift of 3.6. Its progenitor star exploded when the universe was only 1.8 billion years old.
‘A Supernova Discovery Machine’To make these discoveries, the team analyzed imaging data obtained as part of the JWST Advanced Deep Extragalactic Survey (JADES) program. Webb is ideal for finding extremely distant supernovae because their light is stretched into longer wavelengths — a phenomenon known as cosmological redshift.
Prior to Webb’s launch, only a handful of supernovae had been found above a redshift of 2, which corresponds to when the universe was only 3.3 billion years old — just 25% of its current age. The JADES sample contains many supernovae that exploded even further in the past, when the universe was less than 2 billion years old.
Previously, researchers used NASA’s Hubble Space Telescope to view supernovae from when the universe was in the “young adult” stage. With JADES, scientists are seeing supernovae when the universe was in its “teens” or “pre-teens.” In the future, they hope to look back to the “toddler” or “infant” phase of the universe.
To discover the supernovae, the team compared multiple images taken up to one year apart and looked for sources that disappeared or appeared in those images. These objects that vary in observed brightness over time are called transients, and supernovae are a type of transient. In all, the JADES Transient Survey Sample team uncovered about 80 supernovae in a patch of sky only about the thickness of a grain of rice held at arm’s length.
“This is really our first sample of what the high-redshift universe looks like for transient science,” said teammate Justin Pierel, a NASA Einstein Fellow at the Space Telescope Science Institute (STScI) in Baltimore, Maryland. “We are trying to identify whether distant supernovae are fundamentally different from or very much like what we see in the nearby universe.”
Pierel and other STScI researchers provided expert analysis to determine which transients were actually supernovae and which were not, because often they looked very similar.
The team identified a number of high-redshift supernovae, including the farthest one ever spectroscopically confirmed, at a redshift of 3.6. Its progenitor star exploded when the universe was only 1.8 billion years old. It is a so-called core-collapse supernova, an explosion of a massive star.
Image B: Jades Deep Field Transients (NIRCam) This mosaic displays three of about 80 transients, or objects of changing brightness, identified in data from the JADES (JWST Advanced Deep Extragalactic Survey) program. Most of the transients are the result of exploding stars or supernovae. By comparing images taken in 2022 and 2023, astronomers could locate supernovae that recently exploded (like the examples shown in the first two columns), or supernovae that had already exploded and whose light was fading away (third column).
The age of each supernova can be determined from its redshift (designated by ‘z’). The light of the most distant supernova, at a redshift of 3.8, originated when the universe was only 1.7 billion years old. A redshift of 2.845 corresponds to a time 2.3 billion years after the big bang. The closest example, at a redshift of 0.655, shows light that left its galaxy about 6 billion years ago, when the universe was just over half its current age.
Uncovering Distant Type Ia SupernovaeOf particular interest to astrophysicists are Type Ia supernovae. These exploding stars are so predictably bright that they are used to measure far-off cosmic distances and help scientists to calculate the universe’s expansion rate. The team identified at least one Type Ia supernova at a redshift of 2.9. The light from this explosion began traveling to us 11.5 billion years ago when the universe was just 2.3 billion years old. The previous distance record for a spectroscopically confirmed Type Ia supernova was a redshift of 1.95, when the universe was 3.4 billion years old.
Scientists are eager to analyze Type Ia supernovae at high redshifts to see if they all have the same intrinsic brightness, regardless of distance. This is critically important, because if their brightness varies with redshift, they would not be reliable markers for measuring the expansion rate of the universe.
Pierel analyzed this Type Ia supernova found at redshift 2.9 to determine if its intrinsic brightness was different than expected. While this is just the first such object, the results indicate no evidence that Type Ia brightness changes with redshift. More data is needed, but for now, Type Ia supernova-based theories about the universe’s expansion rate and its ultimate fate remain intact. Pierel also presented his findings at the 244th meeting of the American Astronomical Society.
Looking Toward the FutureThe early universe was a very different place with extreme environments. Scientists expect to see ancient supernovae that come from stars that contain far fewer heavy chemical elements than stars like our Sun. Comparing these supernovae with those in the local universe will help astrophysicists understand star formation and supernova explosion mechanisms at these early times.
“We’re essentially opening a new window on the transient universe,” said STScI Fellow Matthew Siebert, who is leading the spectroscopic analysis of the JADES supernovae. “Historically, whenever we’ve done that, we’ve found extremely exciting things — things that we didn’t expect.”
“Because Webb is so sensitive, it’s finding supernovae and other transients almost everywhere it’s pointed,” said JADES team member Eiichi Egami, a research professor at the University of Arizona in Tucson. “This is the first significant step toward more extensive surveys of supernovae with Webb.”
The James Webb Space Telescope is the world’s premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and CSA (Canadian Space Agency).
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Media ContactsLaura Betz – laura.e.betz@nasa.gov, Rob Gutro – rob.gutro@nasa.gov
NASA’s Goddard Space Flight Center, Greenbelt, Md.
Ann Jenkins – jenkins@stsci.edu / Christine Pulliam – cpulliam@stsci.edu
Space Telescope Science Institute, Baltimore, Md.
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Landing on Pluto May Only Be A Hop Skip and Jump Away
There are plenty of crazy ideas for missions in the space exploration community. Some are just better funded than others. One of the early pathways to funding the crazy ideas is NASA’s Institute for Advanced Concepts. In 2017 and again in 2021, it funded a mission study of what most space enthusiasts would consider only a modestly ambitious goal but what those outside the community might consider outlandish—landing on Pluto.
Two major questions stand out in the mission design: How would a probe arriving at Pluto slow down, and what kind of lander would be useful on Pluto itself? The answer to the first is one that is becoming increasingly common on planetary exploration missions: aerobraking.
Pluto has an atmosphere, albeit sparse, as confirmed by the New Horizons mission that whizzed past in 2015. One advantage of the minor planet’s relatively weak gravity is that its low-density atmosphere is almost eight times larger than Earth’s, providing a much bigger target for a fast incoming aerobraking craft to aim for.
Fraser discusses future missions to Pluto.Much of the NIAC Phase I project was focused on the details of that aerobraking system, called the Enveloping Aerodynamic Decelerator (EAD). Combined with a lander, that system makes up the “Entrycraft” that the mission is designed around. Ostensibly, it could alternatively contain an orbiter, and there are plenty of other missions discussing how to insert an orbiter around Pluto. Hence, the main thrust of this paper is to focus on a lander.
After aerobraking and slowing down to a few tens of meters a second, from 14 km/s during its interplanetary cruise phase, the mission would drop its lander payload, then rest on the surface, only to rise again under its own power. The answer to the second question of what kind of lander would be useful on Pluto is – a hopper.
Hoppers have become increasingly popular as an exploration tool everywhere, from the Moon to asteroids. Some apparent advantages would include visiting a wide array of interesting scientific sites and not having to navigate tricky land-based obstacles. Ingenuity, the helicopter that accompanied Perseverance paved the way for the idea, but in other words, the atmosphere isn’t dense enough to support a helicopter. So why not use the current favorite method of almost all spacecraft – rockets?
Fraser discusses the results from New Horizons.A hopper would fire its onboard thrusters to reach the area on Pluto’s surface and then land elsewhere. It could then do some science at its new locale before taking off and doing so again somewhere else. The NIAC Phase I Final Report describes five main scientific objectives of the mission, including understanding the surface geomorphology and running some in-situ chemical analysis. A hopper structure would enable those goals much better than a traditional rover at a relatively low weight cost since Pluto’s gravity is so weak.
Other objectives of the report include mathematical calculations of the trajectory, including the aerobraking itself and the stress and strain it would have on the materials used in the system. The authors, who primarily work for Global Aerospace Corporation and ILC Dover, two private companies, also updated the atmospheric models of Pluto with new New Horizons data, which they then fed into the aerobraking model they used. Designing the lander/hopper, integrating all the scientific and navigation components, and estimating their weights were also part of Phase I.
The original launch window for the mission was planned as 2029 back in 2018, though now, despite receiving a Phase II NIAC grant in 2021, that launch window seems wildly optimistic. Since the mission would require a gravity assist from Jupiter, the next potential launch window would be 2042, with a lander finally reaching the surface of Pluto in the 2050s. That later launch window is likely the only feasible one for the mission, so we might have to wait almost 30 years to see if it will come to fruition. Sometimes crazy ideas take patience – we’ll see if the mission team has enough of that to push it onto the surface of one of the most interesting minor planets in the solar system.
Learn More:
B. Goldman – Pluto Hop, Skip, and Jump
UT – NASA is Now Considering a Pluto Orbiter Mission
UT – Should We Send Humans to Pluto?
UT – New Horizons Team Pieces Together the Best Images They Have of Pluto’s Far Side
Lead Image:
Artist’s depiction of the Pluto Lander mission design.
Credit- B. Goldman / Global Aerospace Corporation
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NASA Wallops to Support Sounding Rocket Launch
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Preparations for Next Moonwalk Simulations Underway (and Underwater) This June 2021 aerial photograph shows the coastal launch range at NASA’s Wallops Flight Facility on Virginia’s Eastern Shore. The Atlantic Ocean is at the right side of this image, and nearby Chincoteague and Assateague islands are at upper left and right, respectively. A subset of NASA’s Goddard Space Flight Center, Wallops is the agency’s only owned-and-operated launch range. Shore replenishment and elevated infrastructure at the range are incorporated into Goddard’s recently approved master plan.Courtesy Patrick J. Hendrickson; used with permission
A suborbital rocket is scheduled for launch the week of June 10-17 from NASA’s launch range at the Wallops Flight Facility in Virginia. This launch is supporting the Missile Defense Agency (MDA), Naval Surface Warfare Center (NSWC), Port Hueneme Division’s White Sands Detachment, other Department of Defense organizations, industry, and academia.
No real-time launch status updates will be available. The launch will not be livestreamed nor will launch status updates be provided during the countdown.
The rocket launch may be visible from the Chesapeake Bay region.
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Preparations for Next Moonwalk Simulations Underway (and Underwater) Food for the Apollo astronauts was not always especially appealing, but thanks to the protocol NASA and Pillsbury came up with, known as the Hazard Analysis and Critical Control Point (HAACP) system, it was always safe.Credit: NASA
Countless NASA technologies turn up in our everyday lives, but one of the space agency’s most important contributions to modern society isn’t a technology at all – it’s the methodology that ensures the safety of the food we eat. Today the safety procedures and regulations for most of the food produced around the world are based on a system NASA created to guarantee safe food for Apollo astronauts journeying to the Moon.
For the Gemini missions, NASA and partner Pillsbury tested the food they were producing at the Manned Spacecraft Center, now Johnson Space Center in Houston, and destroyed entire batches when irregularities were found, a process similar to industry practices of the day. In response to agencywide guidelines from the Apollo Program Office aimed at ensuring the reliability of all critical systems, they altered that method for the Apollo missions.
They focused on identifying any points in the production process where hazards could be introduced, establishing procedures to eliminate or control each of those hazards, and then monitoring each of those points regularly. And they required extensive documentation of all this work. This became the foundation for the Hazard Analysis and Critical Control Point (HACCP) system.
The Apollo missions were humans’ longest and farthest voyages in space, so food for the astronauts had to be guaranteed safe for consumption hundreds of thousands of miles from any medical facility. Credit: NASA
Howard Bauman, the microbiologist leading Pillsbury’s Apollo work, convinced his company to adopt the approach, and he became the leading advocate for its adoption across the food industry. That gradual process took decades, starting with the regulation of certain canned foods in the 1970s and culminating in the 2011 Food Safety Modernization Act, which mandated HACCP-like requirements across all food producers regulated by the U.S. Food and Drug Administration. By then, the U.S. Department of Agriculture was managing HACCP requirements for meat and poultry, while Canada and much of Europe had also put similar rules in place.
The standards also apply to any outside producers who want to export food into a country that requires HACCP, effectively spreading them across the globe.
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“Earthrise” by NASA Astronaut Bill Anders
“Earthrise” by NASA Astronaut Bill Anders
NASA astronaut Bill Anders took this iconic image of Earth rising over the Moon’s horizon on Dec. 24, 1968. Anders, lunar module pilot on the Apollo 8 mission, and fellow astronauts Frank Borman and Jim Lovell became the first humans to orbit the Moon and the first to witness the sight pictured.
After becoming a fighter pilot in the Air Force, Anders was selected as an astronaut by NASA. He was backup pilot for the Gemini XI and Apollo 11 flights, and he was lunar module pilot for Apollo 8 – the first lunar orbit mission in December 1968. Anders passed away on June 7, 2024.
Image Credit: NASA
The Milky Way’s Last Merger Event Was More Recent Than Thought
The Milky Way is only as massive as it is because of collisions and mergers with other galaxies. This is a messy process, and we see the same thing happening with other galaxies throughout the Universe. Currently, we see the Milky Way nibbling at its two satellite galaxies, the Large and Small Magellanic Clouds. Their fate is likely sealed, and they’ll be absorbed into our galaxy.
Researchers thought the last major merger occurred in the Milky Way’s distant past, between 8 and 11 billion years ago. But new research amplifies the idea that it was much more recent: less than 3 billion years ago.
This new insight into our galactic history comes from the ESA’s Gaia mission. Launched in 2013, Gaia is busily mapping 1 billion astronomical objects, mostly stars. It measures them repeatedly, establishing accurate measurements of their positions and motions.
A new paper published in the Monthly Notices of the Royal Astronomical Society presents the findings. It’s titled “The Debris of the ‘Last Major Merger’ is Dynamically Young.” The lead author is Thomas Donlon, a post-doctoral researcher in Physics and Astronomy at the University of Alabama, Huntsville. Donlon has been studying mergers in the Milky Way for several years and has published other work on the matter.
Each time another galaxy collides and merges with the Milky Way, it leaves wrinkles. ‘Wrinkles’ obviously isn’t a scientific term. It’s an umbrella term for several types of morphologies, including phase space folds, caustics, chevrons, and shells. These wrinkles move through different groups of stars within the Milky Way, affecting how the stars move through space. By measuring the positions and velocities of these stars with great precision, Gaia can detect the wrinkles, the imprint of the last major merger.
“We get wrinklier as we age, but our work reveals that the opposite is true for the Milky Way. It’s a sort of cosmic Benjamin Button, getting less wrinkly over time,” said lead author Donlon in a press release. “By looking at how these wrinkles dissipate over time, we can trace when the Milky Way experienced its last big crash—and it turns out this happened billions of years later than we thought.”
The effort to understand the Milky Way’s (MW) last major merger involves different pieces of evidence. One of the pieces of evidence, along with wrinkles, is an Fe/H-rich region where stars follow a highly eccentric orbit. A star’s Fe/H ratio is a chemical fingerprint, and when astronomers find a group of stars with the same fingerprint and the same orbits, it’s evidence of a common origin. This group of stars is sometimes called ‘the Splash.’ The stars in the Splash may have originated in a Fe/H-rich progenitor. They have odd orbits that stand out from their surroundings. Astronomers think they were heated and their orbits altered as a by-product of the merger.
There are two competing explanations for all of the merger evidence.
One says that a progenitor dwarf galaxy named Gaia Sausage/Enceladus (GSE) collided with the MW proto-disk between 8 and 11 billion years ago. The other explanation is that an event called the Virgo Radial Merger (VRM) is responsible for the stars in the inner halo. That collision occurred much more recently, less than 3 billion years ago.
This is a Hubble Space Telescope image of the globular cluster NGC 2808. It might be the old core of the Gaia Sausage. Image Credit: By NASA, ESA, A. Sarajedini (University of Florida) and G. Piotto (University of Padua (Padova)) – http://hubblesite.org/newscenter/archive/releases/2007/2007/18/image/a/ (direct link), Public Domain, https://commons.wikimedia.org/w/index.php?curid=2371715“These two scenarios make different predictions about observable structure in local phase space because the morphology of debris depends on how long it has had to phase mix,” the authors explain in their paper.
The wrinkles in the MW were first identified in Gaia data in 2018 and presented in this paper. “We have observed shapes with different morphologies, such as a spiral similar to a snail’s shell. The existence of these substructures has been observed for the first time thanks to the unprecedented precision of the data brought by Gaia satellite, from the European Space Agency (ESA)”, said Teresa Antoja, the study’s first author, in 2018.
This AI-generated image illustrates the MW’s ‘wrinkles’ from the last major merger event. Image Credit: University of Barcelona.But Gaia has released more data since 2018, and it supports the more recent merger scenario, the Virgo Radial Merger. That data shows that the wrinkles are much more prevalent than the earlier data and the studies based on it suggest.
“For the wrinkles of stars to be as clear as they appear in Gaia data, they must have joined us less than 3 billion years ago—at least 5 billion years later than was previously thought,” said co-author Heidi Jo Newberg, from the Rensselaer Polytechnic Institute. If the wrinkles were much older and conformed to the GSE merger scenario, they’d be more difficult to discern.
“New wrinkles of stars form each time the stars swing back and forth through the center of the Milky Way. If they’d joined us 8 billion years ago, there would be so many wrinkles right next to each other that we would no longer see them as separate features,” Newberg said.
This doesn’t mean there’s no evidence for the more ancient GSE merger. Some of the stars that hint at the ancient merger may be from the more recent VRM merger, and some may still be associated with the GSE merger. It’s challenging to figure out, and simulations play a large role. The researchers in previous work and in this work ran multiple simulations to see how they matched the evidence. “Our goal is to determine the time that has passed since the progenitor of the local phase-space folds collided with the MW disc,” the authors write in their paper.
“We can see how the shapes and number of wrinkles change over time using these simulated mergers. This lets us pinpoint the exact time when the simulation best matches what we see in real Gaia data of the Milky Way today—a method we used in this new study too,” said Thomas.
“By doing this, we found that the wrinkles were likely caused by a dwarf galaxy colliding with the Milky Way around 2.7 billion years ago. We named this event the Virgo Radial Merger.” Those results and the name come from a previous study from 2019.
As Gaia delivers more data with each release, astronomers are getting a better look at the evidence of mergers. It’s becoming clear that the MW has a complex history.
The VRM likely involved more than one entity. It could have brought a whole group of dwarf galaxies and star clusters into the MW at around the same time. As astronomers research the MW’s merger history in greater detail, they hope to determine which of these objects are from the more recent VRM and which are from the ancient GSE.
“The Milky Way’s history is constantly being rewritten at the moment, in no small part thanks to new data from Gaia,” adds Thomas. “Our picture of the Milky Way’s past has changed dramatically from even a decade ago, and I think our understanding of these mergers will continue to change rapidly.”
“This finding improves what we know of the many complicated events that shaped the Milky Way, helping us better understand how galaxies are formed and shaped—our home galaxy in particular,” said Timo Prusti, Project Scientist for Gaia at ESA.
The post The Milky Way’s Last Merger Event Was More Recent Than Thought appeared first on Universe Today.
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The post "Death Star" Black Holes Can Swivel Their Million Light-Year Long Plasma Beams appeared first on Sky & Telescope.