Can life survive a star’s death? Webb telescope can reveal the answer

When stars like our sun die, all that remains is an exposed core — a white dwarf. A planet orbiting a white dwarf presents a promising opportunity to determine if life can survive the death of its star, according to Cornell University researchers.

In a study published in the Astrophysical Journal Letters, they show how NASA’s upcoming James Webb Space Telescope could find signatures of life on Earth-like planets orbiting white dwarfs.

A planet orbiting a small star produces strong atmospheric signals when it passes in front, or “transits,” its host star. White dwarfs push this to the extreme: They are 100 times smaller than our sun, almost as small as Earth, affording astronomers a rare opportunity to characterize rocky planets.

“If rocky planets exist around white dwarfs, we could spot signs of life on them in the next few years,” said corresponding author Lisa Kaltenegger, associate professor of astronomy in the College of Arts and Sciences and director of the Carl Sagan Institute.

Co-lead author Ryan MacDonald, a research associate at the institute, said the James Webb Space Telescope, scheduled to launch in October 2021, is uniquely placed to find signatures of life on rocky exoplanets.

“When observing Earth-like planets orbiting white dwarfs, the James Webb Space Telescope can detect water and carbon dioxide within a matter of hours,” MacDonald said. “Two days of observing time with this powerful telescope would allow the discovery of biosignature gases, such as ozone and methane.”

The discovery of the first transiting giant planet orbiting a white dwarf (WD 1856+534b), announced in a separate paper — led by co-author Andrew Vanderburg, assistant professor at the University of Wisconsin, Madison — proves the existence of planets around white dwarfs. Kaltenegger is a co-author on this paper, as well.

This planet is a gas giant and therefore not able to sustain life. But its existence suggests that smaller rocky planets, which could sustain life, could also exist in the habitable zones of white dwarfs.

“We know now that giant planets can exist around white dwarfs, and evidence stretches back over 100 years showing rocky material polluting light from white dwarfs. There are certainly small rocks in white dwarf systems,” MacDonald said. “It’s a logical leap to imagine a rocky planet like the Earth orbiting a white dwarf.”

The researchers combined state-of-the-art analysis techniques routinely used to detect gases in giant exoplanet atmospheres with the Hubble Space Telescope with model atmospheres of white dwarf planets from previous Cornell research.

NASA’s Transiting Exoplanet Survey Satellite is now looking for such rocky planets around white dwarfs. If and when one of these worlds is found, Kaltenegger and her team have developed the models and tools to identify signs of life in the planet’s atmosphere. The Webb telescope could soon begin this search.

The implications of finding signatures of life on a planet orbiting a white dwarf are profound, Kaltenegger said. Most stars, including our sun, will one day end up as white dwarfs.

“What if the death of the star is not the end for life?” she said. “Could life go on, even once our sun has died? Signs of life on planets orbiting white dwarfs would not only show the incredible tenacity of life, but perhaps also a glimpse into our future.”

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Materials provided by Cornell University. Original written by Kate Blackwood. Note: Content may be edited for style and length.

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How stars form in the smallest galaxies

The question of how small, dwarf galaxies have sustained the formation of new stars over the course of the Universe has long confounded the world’s astronomers. An international research team led by Lund University in Sweden has found that dormant small galaxies can slowly accumulate gas over many billions of years. When this gas suddenly collapses under its own weight, new stars are able to arise.

There are around 2,000 billion galaxies in our Universe and, while our own Milky-Way encompasses between 200 and 400 billion stars, small dwarf galaxies contain only a thousand times less. How stars are formed in these tiny galaxies has long been shrouded in mystery.

However, in a new study published in the research journal Monthly Notices of the Royal Astronomical Society, a research team led from Lund University has established that dwarf galaxies are capable of lying dormant for several billion years before starting to form stars again.

“It is estimated that these dwarf galaxies stopped forming stars around 12 billion years ago. Our study shows that this can be a temporary hiatus,” says Martin Rey, an astrophysicist at Lund University and the leader of the study.

Through high-resolution computer simulations, the researchers demonstrate that star formation in dwarf galaxies ceased as a result of the heating and ionisation from the strong light of newborn stars. Explosions of so-called white dwarfs — small faint stars made of the core that remains when normal-sized stars die -further contribute in preventing the star formation process in dwarf galaxies.

“Our simulations show that dwarf galaxies are able to accumulate fuel in the form of gas, which eventually condenses and gives birth to stars. This explains the observed star formation in existing faint dwarf galaxies that has long puzzled astronomers,” states Martin Rey.

The computer simulations used by the researchers in the study are amongst the most expensive that can be carried out within physics. Each simulation takes as long as two months and requires the equivalent of 40 laptop computers operating around the clock. The work is continuing with the development of methods to better explain the processes behind star formation in our Universe’s smallest galaxies.

“By deepening our understanding of this subject, we gain new insights into the modelling of astrophysical processes such as star explosions, as well as the heating and cooling of cosmic gas. In addition, further work is underway to predict how many such star-forming dwarfs exist in our Universe, and could be discovered by astronomical telescopes” concludes Martin Rey.

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Mystery solved: Bright areas on Ceres come from salty water below

NASA’s Dawn spacecraft gave scientists extraordinary close-up views of the dwarf planet Ceres, which lies in the main asteroid belt between Mars and Jupiter. By the time the mission ended in October 2018, the orbiter had dipped to less than 22 miles (35 kilometers) above the surface, revealing crisp details of the mysterious bright regions Ceres had become known for.

Scientists had figured out that the bright areas were deposits made mostly of sodium carbonate — a compound of sodium, carbon, and oxygen. They likely came from liquid that percolated up to the surface and evaporated, leaving behind a highly reflective salt crust. But what they hadn’t yet determined was where that liquid came from.

By analyzing data collected near the end of the mission, Dawn scientists have concluded that the liquid came from a deep reservoir of brine, or salt-enriched water. By studying Ceres’ gravity, scientists learned more about the dwarf planet’s internal structure and were able to determine that the brine reservoir is about 25 miles (40 kilometers) deep and hundreds of miles wide.

Ceres doesn’t benefit from internal heating generated by gravitational interactions with a large planet, as is the case for some of the icy moons of the outer solar system. But the new research, which focuses on Ceres’ 57-mile-wide (92-kilometer-wide) Occator Crater — home to the most extensive bright areas — confirms that Ceres is a water-rich world like these other icy bodies.

The findings, which also reveal the extent of geologic activity in Occator Crater, appear in a special collection of papers published by Nature Astronomy, Nature Geoscience, and Nature Communications on Aug. 10.

“Dawn accomplished far more than we hoped when it embarked on its extraordinary extraterrestrial expedition,” said Mission Director Marc Rayman of NASA’s Jet Propulsion Laboratory in Southern California. “These exciting new discoveries from the end of its long and productive mission are a wonderful tribute to this remarkable interplanetary explorer.”

Solving the Bright Mystery

Long before Dawn arrived at Ceres in 2015, scientists had noticed diffuse bright regions with telescopes, but their nature was unknown. From its close orbit, Dawn captured images of two distinct, highly reflective areas within Occator Crater, which were subsequently named Cerealia Facula and Vinalia Faculae. (“Faculae” means bright areas.)

Scientists knew that micrometeorites frequently pelt the surface of Ceres, roughing it up and leaving debris. Over time, that sort of action should darken these bright areas. So their brightness indicates that they likely are young. Trying to understand the source of the areas, and how the material could be so new, was a main focus of Dawn’s final extended mission, from 2017 to 2018.

The research not only confirmed that the bright regions are young — some less than 2 million years old; it also found that the geologic activity driving these deposits could be ongoing. This conclusion depended on scientists making a key discovery: salt compounds (sodium chloride chemically bound with water and ammonium chloride) concentrated in Cerealia Facula.

On Ceres’ surface, salts bearing water quickly dehydrate, within hundreds of years. But Dawn’s measurements show they still have water, so the fluids must have reached the surface very recently. This is evidence both for the presence of liquid below the region of Occator Crater and ongoing transfer of material from the deep interior to the surface.

The scientists found two main pathways that allow liquids to reach the surface. “For the large deposit at Cerealia Facula, the bulk of the salts were supplied from a slushy area just beneath the surface that was melted by the heat of the impact that formed the crater about 20 million years ago,” said Dawn Principal Investigator Carol Raymond. “The impact heat subsided after a few million years; however, the impact also created large fractures that could reach the deep, long-lived reservoir, allowing brine to continue percolating to the surface.”

Active Geology: Recent and Unusual

In our solar system, icy geologic activity happens mainly on icy moons, where it is driven by their gravitational interactions with their planets. But that’s not the case with the movement of brines to the surface of Ceres, suggesting that other large ice-rich bodies that are not moons could also be active.

Some evidence of recent liquids in Occator Crater comes from the bright deposits, but other clues come from an assortment of interesting conical hills reminiscent of Earth’s pingos — small ice mountains in polar regions formed by frozen pressurized groundwater. Such features have been spotted on Mars, but the discovery of them on Ceres marks the first time they’ve been observed on a dwarf planet.

On a larger scale, scientists were able to map the density of Ceres’ crust structure as a function of depth — a first for an ice-rich planetary body. Using gravity measurements, they found Ceres’ crustal density increases significantly with depth, way beyond the simple effect of pressure. Researchers inferred that at the same time Ceres’ reservoir is freezing, salt and mud are incorporating into the lower part of the crust.

Dawn is the only spacecraft ever to orbit two extraterrestrial destinations — Ceres and the giant asteroid Vesta — thanks to its efficient ion propulsion system. When Dawn used the last of a key fuel, hydrazine, for a system that controls its orientation, it was neither able to point to Earth for communications nor to point its solar arrays at the Sun to produce electrical power. Because Ceres was found to have organic materials on its surface and liquid below the surface, planetary protection rules required Dawn to be placed in a long-duration orbit that will prevent it from impacting the dwarf planet for decades.

JPL, a division of Caltech in Pasadena, California, manages Dawn’s mission for NASA’s Science Mission Directorate in Washington. Dawn is a project of the directorate’s Discovery Program, managed by NASA’s Marshall Space Flight Center in Huntsville, Alabama. JPL is responsible for overall Dawn mission science. Northrop Grumman in Dulles, Virginia, designed and built the spacecraft. The German Aerospace Center, Max Planck Institute for Solar System Research, Italian Space Agency and Italian National Astrophysical Institute are international partners on the mission team.

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White dwarfs reveal new insights into the origin of carbon in the universe

A new analysis of white dwarf stars supports their role as a key source of carbon, an element crucial to all life, in the Milky Way and other galaxies.

Approximately 90 percent of all stars end their lives as white dwarfs, very dense stellar remnants that gradually cool and dim over billions of years. With their final few breaths before they collapse, however, these stars leave an important legacy, spreading their ashes into the surrounding space through stellar winds enriched with chemical elements, including carbon, newly synthesized in the star’s deep interior during the last stages before its death.

Every carbon atom in the universe was created by stars, through the fusion of three helium nuclei. But astrophysicists still debate which types of stars are the primary source of the carbon in our own galaxy, the Milky Way. Some studies favor low-mass stars that blew off their envelopes in stellar winds and became white dwarfs, while others favor massive stars that eventually exploded as supernovae.

In the new study, published July 6 in Nature Astronomy, an international team of astronomers discovered and analyzed white dwarfs in open star clusters in the Milky Way, and their findings help shed light on the origin of the carbon in our galaxy. Open star clusters are groups of up to a few thousand stars, formed from the same giant molecular cloud and roughly the same age, and held together by mutual gravitational attraction. The study was based on astronomical observations conducted in 2018 at the W. M. Keck Observatory in Hawaii and led by coauthor Enrico Ramirez-Ruiz, professor of astronomy and astrophysics at UC Santa Cruz.

“From the analysis of the observed Keck spectra, it was possible to measure the masses of the white dwarfs. Using the theory of stellar evolution, we were able to trace back to the progenitor stars and derive their masses at birth,” Ramirez-Ruiz explained.

The relationship between the initial masses of stars and their final masses as white dwarfs is known as the initial-final mass relation, a fundamental diagnostic in astrophysics that integrates information from the entire life cycles of stars, linking birth to death. In general, the more massive the star at birth, the more massive the white dwarf left at its death, and this trend has been supported on both observational and theoretical grounds.

But analysis of the newly discovered white dwarfs in old open clusters gave a surprising result: the masses of these white dwarfs were notably larger than expected, putting a “kink” in the initial-final mass relation for stars with initial masses in a certain range.

“Our study interprets this kink in the initial-final mass relationship as the signature of the synthesis of carbon made by low-mass stars in the Milky Way,” said lead author Paola Marigo at the University of Padua in Italy.

In the last phases of their lives, stars twice as massive as our Sun produced new carbon atoms in their hot interiors, transported them to the surface, and finally spread them into the interstellar medium through gentle stellar winds. The team’s detailed stellar models indicate that the stripping of the carbon-rich outer mantle occurred slowly enough to allow the central cores of these stars, the future white dwarfs, to grow appreciably in mass.

Analyzing the initial-final mass relation around the kink, the researchers concluded that stars bigger than 2 solar masses also contributed to the galactic enrichment of carbon, while stars of less than 1.5 solar masses did not. In other words, 1.5 solar masses represents the minimum mass for a star to spread carbon-enriched ashes upon its death.

These findings place stringent constraints on how and when carbon, the element essential to life on Earth, was produced by the stars of our galaxy, eventually ending up trapped in the raw material from which the Sun and its planetary system were formed 4.6 billion years ago.

“Now we know that the carbon came from stars with a birth mass of not less than roughly 1.5 solar masses,” said Marigo.

Coauthor Pier-Emmanuel Tremblay at University of Warwick said, “One of most exciting aspects of this research is that it impacts the age of known white dwarfs, which are essential cosmic probes to understand the formation history of the Milky Way. The initial-to-final mass relation is also what sets the lower mass limit for supernovae, the gigantic explosions seen at large distances and that are really important to understand the nature of the universe.”

By combining the theories of cosmology and stellar evolution, the researchers concluded that bright carbon-rich stars close to their death, quite similar to the progenitors of the white dwarfs analyzed in this study, are presently contributing to a vast amount of the light emitted by very distant galaxies. This light, carrying the signature of newly produced carbon, is routinely collected by large telescopes to probe the evolution of cosmic structures. A reliable interpretation of this light depends on understanding the synthesis of carbon in stars.

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In a first, NASA measures wind speed on a brown dwarf

For the first time, scientists have directly measured wind speed on a brown dwarf, an object larger than Jupiter (the largest planet in our solar system) but not quite massive enough to become a star. To achieve the finding, they used a new method that could also be applied to learn about the atmospheres of gas-dominated planets outside our solar system.

Described in a paper in the journal Science, the work combines observations by a group of radio telescopes with data from NASA’s recently retired infrared observatory, the Spitzer Space Telescope, managed by the agency’s Jet Propulsion Laboratory in Southern California.

Officially named 2MASS J10475385+2124234, the target of the new study was a brown dwarf located 32 light-years from Earth — a stone’s throw away, cosmically speaking. The researchers detected winds moving around the planet at 1,425 mph (2,293 kph). For comparison, Neptune’s atmosphere features the fastest winds in the solar system, which whip through at more than 1,200 mph (about 2,000 kph).

Measuring wind speed on Earth means clocking the motion of our gaseous atmosphere relative to the planet’s solid surface. But brown dwarfs are composed almost entirely of gas, so “wind” refers to something slightly different. The upper layers of a brown dwarf are where portions of the gas can move independently. At a certain depth, the pressure becomes so intense that the gas behaves like a single, solid ball that is considered the object’s interior. As the interior rotates, it pulls the upper layers — the atmosphere -along so that the two are almost in synch.

In their study, the researchers measured the slight difference in speed of the brown dwarf’s atmosphere relative to its interior. With an atmospheric temperature of over 1,100 degrees Fahrenheit (600 degrees Celsius), this particular brown dwarf radiates a substantial amount of infrared light. Coupled with its close proximity to Earth, this characteristic made it possible for Spitzer to detect features in the brown dwarf’s atmosphere as they rotate in and out of view. The team used those features to clock the atmospheric rotation speed.

To determine the speed of the interior, they focused on the brown dwarf’s magnetic field. A relatively recent discovery found that the interiors of brown dwarfs generate strong magnetic fields. As the brown dwarf rotates, the magnetic field accelerates charged particles that in turn produce radio waves, which the researchers detected with the radio telescopes in the Karl G. Jansky Very Large Array in New Mexico.

Planetary Atmospheres

The new study is the first to demonstrate this comparative method for measuring wind speed on a brown dwarf. To gauge its accuracy, the group tested the technique using infrared and radio observations of Jupiter, which is also composed mostly of gas and has a physical structure similar to a small brown dwarf. The team compared the rotation rates of Jupiter’s atmosphere and interior using data that was similar to what they were able to collect for the much more distant brown dwarf. They then confirmed their calculation for Jupiter’s wind speed using more detailed data collected by probes that have studied Jupiter up close, thus demonstrating that their approach for the brown dwarf worked.

Scientists have previously used Spitzer to infer the presence of winds on exoplanets and brown dwarfs based on variations in the brightness of their atmospheres in infrared light. And data from the High Accuracy Radial velocity Planet Searcher (HARPS) — an instrument on the European Southern Observatory’s La Silla telescope in Chile — has been used to make a direct measurement of wind speeds on a distant planet.

But the new paper represents the first time scientists have directly compared the atmospheric speed with the speed of a brown dwarf’s interior. The method employed could be applied to other brown dwarfs or to large planets if the conditions are right, according to the authors.

“We think this technique could be really valuable to providing insight into the dynamics of exoplanet atmospheres,” said lead author Katelyn Allers, an associate professor of physics and astronomy at Bucknell University in Lewisburg, Pennsylvania. “What’s really exciting is being able to learn about how the chemistry, the atmospheric dynamics and the environment around an object are interconnected, and the prospect of getting a really comprehensive view into these worlds.”

The Spitzer Space Telescope was decomissioned on Jan. 30, 2020, after more than 16 years in space. JPL managed Spitzer mission operations for NASA’s Science Mission Directorate in Washington. Spitzer science data continue to be analyzed by the science community via the Spitzer data archive located at the Infrared Science Archive housed at IPAC at Caltech. Science operations were conducted at the Spitzer Science Center at IPAC at Caltech in Pasadena. Spacecraft operations were based at Lockheed Martin Space in Littleton, Colorado. Caltech manages JPL for NASA.

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Two stars merged to form massive white dwarf

A massive white dwarf star with a bizarre carbon-rich atmosphere could be two white dwarfs merged together according to an international team led by University of Warwick astronomers, and only narrowly avoided destruction.

They have discovered an unusual ultra-massive white dwarf around 150 light years from us with an atmospheric composition never seen before, the first time that a merged white dwarf has been identified using its atmospheric composition as a clue.

The discovery, published today (2 March) in the journal Nature Astronomy, could raise new questions about the evolution of massive white dwarf stars and on the number of supernovae in our galaxy.

This star, named WDJ0551+4135, was identified in a survey of data from the European Space Agency’s Gaia telescope. The astronomers followed up with spectroscopy taken using the William Herschel Telescope, focusing on those white dwarfs identified as particularly massive — a feat made possible by the Gaia mission. By breaking down the light emitted by the star, the astronomers were able to identify the chemical composition of its atmosphere and found that it had an unusually high level of carbon present.

Lead author Dr Mark Hollands, from the University of Warwick Department of Physics, said: “This star stood out as something we had never seen before. You might expect to see an outer layer of hydrogen, sometimes mixed with helium, or just a mix of helium and carbon. You don’t expect to see this combination of hydrogen and carbon at the same time as there should be a thick layer of helium in between that prohibits that. When we looked at it, it didn’t make any sense.”

To solve the puzzle, the astronomers turned detective to uncover the star’s true origins.

White dwarfs are the remains of stars like our own Sun that have burnt out all their fuel and shed their outer layers. Most are relatively lightweight, around 0.6 times the mass of our Sun, but this one weighs in at 1.14 solar masses, nearly twice the average mass. Despite being heavier than our Sun, it is compacted into two-thirds the diameter of Earth.

The age of the white dwarf is also a clue. Older stars orbit the Milky Way faster than younger ones, and this object is moving faster than 99% of the other nearby white dwarfs with the same cooling age, suggesting that this star is older than it looks.

Dr Hollands adds: “We have a composition that we can’t explain through normal stellar evolution, a mass twice the average for a white dwarf, and a kinematic age older than that inferred from cooling. We’re pretty sure of how one star forms one white dwarf and it shouldn’t do this. The only way you can explain it is if it was formed through a merger of two white dwarfs.”

The theory is that when one star in a binary system expands at the end of its life it will envelope its partner, drawing its orbit closer as the first star shrinks. The same will happen when the other star expands. Over billions of years, gravitational wave emission will shrink the orbit further, to the point that the stars merge together.

While white dwarf mergers have been predicted to occur, this one would be particularly unusual. Most of the mergers in our galaxy will be between stars with different masses, whereas this merger appears to be between two similarly sized stars. There is also a limit to how big the resulting white dwarf can be: at more than 1.4 solar masses it is thought that it would explode in a supernova though it may be possible for that these explosions can occur at slightly lower masses, so this star is useful in demonstrating how massive a white dwarf can get and still survive.

Because the merging process restarts the cooling of the star, it is difficult to determine how old it is. The white dwarf probably merged around 1.3 billion years ago but the two original white dwarfs may have existed for many billions of years prior.

It is one of only a handful of merged white dwarfs to be identified so far, and the only one via its composition.

Dr Hollands adds: “There aren’t that many white dwarfs this massive, although there are more than you would expect to see which implies that some of them were probably formed by mergers.

“In the future we may be able to use a technique called asteroseismology to learn about the white dwarf’s core composition from its stellar pulsations, which would be an independent method confirming this star formed from a merger.

“Maybe the most exciting aspect of this star is that it must have just about failed to explode as a supernova — these gargantuan explosions are really important in mapping the structure of the Universe, as they can be detected out to very large distances. However, there remains much uncertainty about what kind of stellar systems make it to the supernova stage. Strange as it may sound, measuring the properties of this ‘failed’ supernova, and future look-alikes, is telling us a lot about the pathways to thermonuclear self-annihilation.”

The research was funded by the European Research Council and the Science and Technologies Facilities Council (STFC) part of UK Research and Innovation (UKRI).

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When the milky way collided with dwarf galaxy gaia-enceladus

The dwarf galaxy Gaia-Enceladus collided with the Milky Way probably approximately 11.5 billion years ago. A team of researchers including scientists from the Max Planck Institute for Solar System Research in Germany for the first time used a single star affected by the collision as a clue for dating. Using observational data from ground-based observatories and space telescopes, the scientists led by the University of Birmingham were able to determine the age of the star and the role it played in the collision. The research group describes its results in today’s issue of Nature Astronomy.

On cosmic time scales, the colliding and merging of galaxies is not uncommon. Even if both galaxies involved are of very different sizes, such a collision leaves clear traces in the larger one. For example, the smaller galaxy introduces stars with a different chemical composition, the motion of many stars is altered, and myriads of new stars are formed.

The Milky Way has encountered several other galaxies in its 13.5 billion-year history. One of them is the dwarf galaxy Gaia-Enceladus. To understand how this event affected our galaxy and changed it permanently, it is important to reliably date the collision. To this end, the researchers led by Prof. Dr. Bill Chaplin of the University of Birmingham turned their attention to a single star: ? Indi is found in the constellation Indus; with an apparent brightness comparable to that of Uranus, it is visible even to the naked eye and can be easily studied in detail.

“The space telescope TESS collected data from ? Indi already in its first month of scientific operation,” says Dr. Saskia Hekker, head of the research group “Stellar Ages and Galactic Evolution (SAGE)” at MPS and co-author of the new study. The space telescope was launched in 2018 to perform a full-sky survey and characterize as many stars as possible. “The data from TESS allow us to determine the age of the star very accurately,” Hekker adds.

Moreover, ? Indi provided clues on the history of the collision with the dwarf galaxy Gaia-Enceladus. To reconstruct its role in the collision, the research group evaluated numerous data sets on ? Indi obtained with the help of the spectrographs HARPS (High Accuracy Radial velocity Planet Searcher) and FEROS (Fiber-fed Extended Range Optical Spectrograph) of the European Southern Observatory, the Galaxy Evolution Experiment of the Apache Point Observatory in New Mexico, and ESA’s Gaia Space Telescope. This allowed them to specify both the chemical composition of the star and its movement within the galaxy with great precision.

The cosmic detective work produced a clear picture: v Indi has been part of the halo, the outer region of the Milky Way, and the collision changed its trajectory. “Since the motion of v Indi was affected by the collision, it must have taken place when the star was already formed,” Chaplin explains the line of argument. The age of the star therefore puts a constraint on the time of the collision.

To determine the age of a star, researchers use its natural oscillations, which can be observed as brightness fluctuations. “Similar to the way seismic waves on Earth allow conclusions about the interior of our planet, stellar oscillations help us to reveal the internal structure and composition of the star and thus its age,” explains co-author Dr. Nathalie Themessl.

The calculations carried out by MPS researchers and other research groups showed that with a probability of 95 percent the galaxy merger must have occurred 13.2 billion years ago. With a probability of 68 percent, the collision took place approximately 11.5 billion years ago. “This chronological classification not only helps us to understand how the collision changed our galaxy,” says Hekker. “It also gives us a sense, of how collisions and mergers impacted other galaxies and influenced their evolution.”

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