4.02.2024
James Webb Space Telescope makes rare detection of 2 exoplanets orbiting dead stars
"This offers our first chance to see what a planetary system looks like after its star dies."
An illustration shows a Jupiter like world orbiting a dead whire dwarf star. (Image credit: Robert Lea (created with Canva))
The James Webb Space Telescope (JWST) has already proven itself adept at peering into the past by imaging objects at tremendous distances, but a new breakthrough may have seen the powerful instrument act almost like a scientific crystal ball, staring into the far future of the solar system.
The JWST performed its prognostication when it made a possible rare direct direction of two extrasolar planets, or "exoplanets," orbiting two different dead stars, or "white dwarfs."
Not only do the planets strongly resemble solar system gas giants Jupiter and Saturn, but the white dwarfs also serve as analogs to the sun's destiny. When the sun transforms into a white dwarf itself, the change will likely destroy the inner solar system planets — all the way out to Jupiter.
"Very few planets have been discovered around white dwarf stars. What is extraordinary about these two candidate planets is that they are more similar to planets in our outer solar system in temperature, age, mass and orbital separation than any planets previously found," Susan Mullaly, lead author of the research, which is yet to be peer-reviewed, and an astronomer at the Space Telescope Science Institute, told Space.com. "This offers our first chance to see what a planetary system looks like after its star dies."
A snapshot of our future
The planet candidates were directly observed by the JWST's Mid-Infrared Instrument (MIRI) as they orbit the white dwarfs WD 1202-232 and WD 2105-82. One exoplanet candidate is located at a distance from its white dwarf host that's equal to about 11.5 times the distance between the Earth and the sun. The other candidate sits further from its dead stellar parent, at a distance of about 34.5 times the separation between our planet and star.
The masses of the planets are currently uncertain, with Mullaly and colleagues estimating them to be between 1 and 7 times that of Jupiter, the most massive planet in the solar system.
When the sun exhausts its fuel supply for the nuclear fusion processes occuring at its core in around 5 billion years, it will swell up as a red giant. Nuclear fusion, however, will continue in its outer layers. This will see those outer layers of our star reach out as far as Mars, swallowing Mercury, Venus, Earth, and possibly, the Red Planet itself. Eventually, these outer layers will cool, leaving a smoldering stellar core, now a white dwarf, surrounded by a planetary nebula of exhausted stellar matter.
These exoplanet detections, however, hint at what could happen to the planets beyond Mars, the gas giants Jupiter and Saturn, when the sun dies.
"Our sun is expected to turn into a white dwarf star in 5 billion years," Mullaly said. "We expect planets to drift outward, into wider orbits, after a star dies. So, if you wind back the clock on these candidate planets, you would expect these to have had orbital separations similar to Jupiter and Saturn.
"If we are able to confirm these planets, they will provide direct evidence that planets like Jupiter and Saturn can survive the death of their host star."
The two exoplanets as seen around their white dwarf stars by the JWST instrument MIRI. (Image credit: Mulaney, et al, 2024)
Further, the white dwarfs at the heart of this discovery are polluted with elements heavier than hydrogen and helium, which astronomers call "metals." This could hint at what will happen to the bodies in the asteroid belt between Mars and Jupiter after the sun dies.
"We suspect that the giant planets cause the metal pollution by driving comets and asteroids onto the surface of the stars," Mullaly explained. "The existence of these planets strengthens the connection between the metal pollution and planets. Since 25% to 50% of white dwarfs show this kind of pollution, it means that giant planets are common around white dwarf stars."
As such, any asteroids that do survive the death of the sun could find themselves pelted at its corpse by Jupiter and Saturn.
The dual discovery is impressive beyond what it predicts for the future of our planetary system — it also simply represents a rare scientific achievement.
A rare direct exoplanet detection
Since the discovery of the first exoplanets in the mid-1990s, astronomers have discovered around 5,000 worlds orbiting stars outside the solar system. According to the Planetary Society, as of April 2020, only 50 of these exoplanets had been discovered with direct imaging.
That is because any light from a planet at such vast distances is usually overwhelmed by the intense light from that planet's parent star, making directly spotting an exoplanet similar to sighting a firefly sitting on the lit lamp of a lighthouse.
As a result, exoplanets are usually seen by the effect they have on the light of their star, either by causing a dip in light output as they cross, or "transit," the star's face or through a "wobble" motion created as the planet gravitationally tugs on the star.
"We directly imaged these two exoplanets, which means we took their picture and are seeing the light produced by the planet itself," Mullaly said. "Most exoplanets that have been discovered have been found using the transit methodor by measuring the motion of the star. These indirect methods tend to favor planets much closer to the star. Direct imaging is better at finding planets farther away from the star, at wider orbital separations."
She explained that, by spotting these planets directly, the JWST has opened up the possibility of studying these worlds further; scientists can now start investigating things like the composition of the planets' atmospheres and directly measure their masses and temperatures.
Mullaly added that not everything she and her team discovered about these exoplanets was expected, and that these quirks could change how astronomers think about exoplanets like these in general.
Alternatively, the strange features of the targeted worlds could offer tantalizing hints in the direction of long-sought exomoons.
"If these are planets, then it is surprising that they are not as red in the mid-infrared as we might expect. The amount of light collected by JWST at 5 and 7 microns is brighter than we might expect for both exoplanet candidates given their age and how bright they are at 15 microns," Mullaly concluded. "This might challenge our understanding of the physics and chemistry of exoplanet atmospheres.
"Or maybe it means there is another source of light, like a heated moon orbiting the planet."
The team's research is available as a preprint on the research repository site arXiv.
Quelle: SC
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Update: 7.02.2024
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James Webb Space Telescope could target tiny bright galaxies to shine light on dark matter
"The discovery of patches of small, bright galaxies in the early universe would confirm that we are on the right track with the cold dark matter model."
An image of Stephan's Quintet taken by the James Webb Space Telescope. (Image credit: NASA, ESA, CSA, STScI)
If the James Webb Space Telescope (JWST) investigates tiny and bright galaxies in the early universe, it may be able to to shine a light on dark matter — the universe's most mysterious stuff.
Such is the conclusion reached by scientists from the University of California, who ran a simulation of the cosmos that tracks the formation of small galaxies — starting as far back as shortly after the Big Bang. This appears to have upped the ante for the JWST.
Small galaxies, also known as dwarf galaxies, are distributed throughout the cosmos, and scientists have suggested they may represent some of the earliest galaxies to have formed. This means dwarf galaxies have often been considered key in studying the origins and evolution of the universe.
The problem has been, however, that these galaxies don't always match what astronomers expect to observe. For instance, some spin faster than expected, and others are less dense than simulations suggest they should be. This is where dark matter comes in.
These puzzling contradictions, scientists think, could exist because researchers haven't factored into their simulations the combination of gas and dark matter.
The team's new simulation thus factored in those interactions between dark matter and gas, finding that early galaxies that are created smaller and much brighter than those in simulations that neglect the interplay. The scientists also saw the galaxies growing more rapidly than other teams have seen.
Hence, the UCLA team thinks astronomers should start hunting small, early galaxies that are much brighter than expected using the JWST and other telescopes. Should these galaxies fail to turn up, well, then something could actually just be wrong with our theories of dark matter.
In the dark about dark matter
Dark matter is such a headache for scientists because it doesn't interact with light, which makes it effectively invisible to us.
The matter that makes up stars, gas, planets, our bodies, your next door cat and pretty much everything you see around you is comprised of atoms made of electrons, protons and neutrons. These are called "baryons," and they do interact with light. Thus, scientists realized, dark matter must be made up of something else — something "non-baryonic."
All of this means that, despite the fact that dark matter accounts for around 85% of the mass in the universe, scientists can't detect it directly and have no solid idea what it is made of.
Because dark matter has mass, it does interact with gravity. That means its presence can be inferred by how these gravitational effects impact baryonic matter and indeed light.
The whole concept of dark matter was initially postulated, in fact, because galaxies are spinning so rapidly that the gravitational influence of their baryonic matter alone couldn't prevent them from flying apart. It is the influence of unseen dark matter that gravitationally "glues" galaxies together, scientists believe.
Scientists further posit that most galaxies are surrounded by vast haloes of dark matter that extend way beyond their visible star, gas and dust content. They also think these haloes may have been integral to the galaxies' formation and evolution.
In the currently favored model of universal evolution, the "standard cosmological model," the gravitational influence of dark matter clumps that existed in the universe 13 billion years ago managed to draw in baryonic matter made of
normal old atoms.
Once this "ordinary matter" grew massive enough, it collapsed to birth the first stars. Along with dark matter, these first stars drew in more baryonic matter, creating the galaxies around them.
The standard model features a form of dark matter called "cold dark matter," which gets its name not because it is chilly but because it moves slower than the speed of light (heat being a measure of how fast particles are moving). The gathering of stars and galaxies in the standard cosmological model would also be slow if they were dependent on cold dark matter.
Baryonic matter in the form of hydrogen and helium gas from the Big Bang would have streamed past those slow-moving dark matter clumps at supersonic speeds in this early stage of the universe's history. That is, until the matter got ultimately ensnared, then collected together to form galaxies.
"Indeed, in models that do not take streaming into account, this is exactly what happens," Claire Williams, team member and a doctoral student at UCLA, said in a statement. "Gas is attracted to the gravitational pull of dark matter, forms clumps and knots so dense that hydrogen fusion can occur, and thus forms stars like our sun."
Williams and colleagues found that, when this so-called streaming effect between dark and ordinary matter is accounted for in their simulation, part of the aptly named "Supersonic Project," gas landed far from dark matter and growing galaxies. This prevented the immediate formation of stars.
Millions of years after this, the gas eventually fell back into the galaxies, triggering an intense spate of star formation called "starburst," creating galaxies that had many more young, hot stars than ordinary small galaxies. For a time, those starburst galaxies should've shone much brighter than other galaxies.
"While the streaming suppressed star formation in the smallest galaxies, it also boosted star formation in dwarf galaxies, causing them to outshine the non-streaming patches of the universe," Williams explained. "We predict that the JWST telescope will be able to find regions of the universe where galaxies will be brighter, heightened by this velocity.
"The fact that they should be so bright might make it easier for the telescope to discover these small galaxies, which are typically extremely hard to detect only 375 million years after the Big Bang."
The fact that dark matter is effectively invisible means these small, bright galaxies in the early universe would make a good proxy by which to test the cold dark matter concept. Failure to detect them may mean scientists have to turn to other theories.
"The discovery of patches of small, bright galaxies in the early universe would confirm that we are on the right track with the cold dark matter model because only the velocity between two kinds of matter can produce the type of galaxy we’re looking for," Smadar Naoz, Supersonic team leader and a UCLA physics and astronomy professor, said in the statement. "If dark matter does not behave like standard cold dark matter and the streaming effect isn’t present, then these bright dwarf galaxies won’t be found, and we need to go back to the drawing board."
Quelle: SC
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Update: 14.02.2024
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James Webb Space Telescope tracks a galaxy's history back to just after the Big Bang
"In looking so deeply and seeing so clearly, we've been able to, effectively, go back in time."
(left) Wolf–Lundmark–Melotte as seen by the Spitzer Space Telescope (Right) an improved view of the galaxy seen by the james Webb Space Telescope (Image credit: NASA, ESA, CSA, IPAC, Kristen McQuinn/Rutgers University)
"A long time ago, in a galaxy not so far away..."
Astronomers have used the James Webb Space Telescope (JWST) to map out the history of stars in a low-mass dwarf galaxy that resembles galaxies that filled the early universe. The research could help better understand how star formationrates have changed over the last 13 billion or so years since time began.
The team, led by Rutgers University-New Brunswick astronomer Kristen McQuinn, zoomed in on the galaxy Wolf–Lundmark–Melotte (WLM) with the JWST to obtain the most accurate picture yet of this isolated realm in the cosmos.
A neighbor of the Milky Way, WLM dwells at the edge of our galaxy's local group around 3 million light-years away. It's actively forming stars, and also hosts ancient stars believed to have formed some 13 billion years ago, only around 800 million years after the Big Bang happened.
Because low-mass galaxies like this are thought to have dominated the early universe, they make an excellent proxy for researchers like McQuinn aiming to study early star formation rates.
"In looking so deeply and seeing so clearly, we've been able to, effectively, go back in time," McQuinn said. “You’re basically going on a kind of archaeological dig to find the very low-mass stars that were formed early in the history of the universe.”
The observing power of the JWST has finally allowed astronomers to zoom in on these faint galaxies like never before.
Studying small galaxies has big scientific rewards
Low-mass galaxies like WLM are faint and widespread across the sky, comprising the majority of galaxies in the Milky Way's local group. WLM has a privileged position in the dumbbell-shaped local group, however, because existing at the edge of this gathering has kept it isolated and has prevented the gravitational influence of other galaxies from ravaging its stellar population.
This, plus the fact that it is a dynamic, complex system replete with gas and dust, makes WLM a fascinating target for astronomers.
To determine WLM's star formation history and the rate at which stars have been born across different epochs, the JWST zoomed in on patches of sky corresponding with WLM and containing hundreds of thousands of individual stars. The team then measured these stars' colors and brightnesses to determine their ages.
"We can use what we know about stellar evolution and what these colors and brightnesses indicate to age the galaxy’s stars basically," McQuinn said.
She and her colleagues turned to the Amarel high-performance computing cluster, managed by the Rutgers Office of Advanced Research Computing, to possess the JWST's data. This allowed them to count the stars of different ages and thus chart the birth rate of stars over the history of the universe.
"What you end up with is a sense of how old this structure that you’re looking at is," McQuinn said.
The ebb and flow of star birth
The researchers saw that the production of stars ebbed and flowed per the data, with WLM producing the most stars over a period of 3 billion years that started between 2 billion and 4 billion years after the Big Bang.
This star formation was halted before starting up again; McQuinn attributes this pause to conditions specific to the early universe.
"The universe back then was really hot. We think the temperature of the universe ended up heating the gas in this galaxy and kind of turned off star formation for a while," she said. "The cool-down period lasted a few billion years, and then star formation proceeded again."
The new research effectively demonstrates the range of uses astronomers have for the JWST, which launched on Christmas Day 2021 and started sending back data in the summer of 2022.
Additionally, McQuinn thinks the major computation effort from the Amarel high-performance computing cluster, in calibrating and processing JWST data to reach these results, demonstrates several processing procedures that could benefit the wider scientific community.
The team's research is published in the Astrophysical Journal.
Quelle: SC
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Update: 16.02.2024
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Galaxies that shouldn’t exist keep being discovered by JWST
A bright red speck appears against the backdrop of a space photo, but astronomers say it shouldn’t be there.
But there it is. Published today in the journal Nature, an international research team led by Karl Glazebrook from Swinburne University of Technology in Melbourne says the light reaching Earth from this galaxy – named JWST-7329 – is 11.5 billion years old and comes from an ancient assembly of stars that likely formed 13bn years ago.
It doesn’t make sense because it’s been thought until now there wasn’t enough dark matter in the early universe to prompt their formation.
JWST-7329: a rare massive galaxy that formed very early in the Universe. Credit: Supplied
Current understanding of what grows a galaxy suggests that dark matter halos, which are fields of invisible material in space, coalesce and collect stars and galaxies within their structure.
It’s only because of the JWST that the team has been able to clarify what the red speck was. In 7 years of long observations using the ground-based Keck (Hawaii, US) and Very Large Telescopes (Chile) all they could see was a faint red smudge.
“NASA’s James Webb Space Telescope, it’s been such an incredible thing. I’ve been wanting it for the last 30 years and it’s delivering on all those dreams we’ve had,” Glazebrook tells Cosmos.
“This is something we’ve been working on over the years: deeper and deeper surveys looking for the oldest and most massive galaxies that formed.
“We did the calculations of how old it is and it’s way beyond the bounds of what’s reasonable to form in the cold dark matter dominated universe. It’s really a huge puzzle.
“I hope it points to the revision of how dark matter halos assemble and how galaxies are made.”
Not the first ‘impossible galaxy’, not the last either
As impossible as galaxy ZF-UDS-732 is, it’s not the first so-called “impossible galaxy” to be spotted.
Earlier this month, a team led by Arizona State University (ASU) researchers found a dwarf galaxy – named PEARLSDG – in a region of space 98 million light years away expected to house, well, nothing much.
An isolated dwarf galaxy should either continue making new stars or interact with another nearby galaxy. PEARLSDG does neither.
“These types of isolated quiescent dwarf galaxies haven’t really been seen before except for relatively few cases. They are not really expected to exist given our current understanding of galaxy evolution, so the fact that we see this object helps us improve our theories for galaxy formation,” said ASU research scientist Tim Carleton, who led the team that found PEARLSDG.
“Generally, dwarf galaxies that are out there by themselves are continuing to form new stars.”
Quelle: COSMOS
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Update: 21.02.2024
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Webb telescope spots hints that Eris, Makemake are geologically active
Webb measured isotopes at the edge of the Solar System, hinting at chemistry.
Artist's conceptions of what the surfaces of two dwarf planets might look like.
Active geology—and the large-scale chemistry it can drive—requires significant amounts of heat. Dwarf planets near the far edges of the Solar System, like Pluto and other Kuiper Belt objects, formed from frigid, icy materials and have generally never transited close enough to the Sun to warm up considerably. Any heat left over from their formation was likely long since lost to space.
Yet Pluto turned out to be a world rich in geological features, some of which implied ongoing resurfacing of the dwarf planet's surface. Last week, researchers reported that the same might be true for other dwarf planets in the Kuiper Belt. Indications come thanks to the capabilities of the Webb telescope, which was able to resolve differences in the hydrogen isotopes found on the chemicals that populate the surface of Eris and Makemake.
Cold and distant
Kuiper Belt objects are natives of the distant Solar System, forming far enough from the warmth of the Sun that many materials that are gasses in the inner planets—things like nitrogen, methane, and carbon dioxide—are solid ices. Many of these bodies formed far enough from the gravitational influence of the eight major planets that they have never made a trip into the warmer inner Solar System. In addition, because there was much less material that far from the Sun, most of the bodies are quite small.
While they would have started off hot due to the process by which they formed, their small size means a large surface-to-volume ratio, allowing internal heat to radiate out to space relatively quickly. Since then, any heat has come from rare collision events or the decay of radioactive isotopes.
Yet New Horizons' visit to Pluto made it clear that it doesn't take much heat to drive active geology, although seasonal changes in sunlight are likely to account for some of its features. Sunlight is less likely to be an influence for worlds like Makemake, which orbits at a distance one and a half times Pluto's closest approach to the Sun. Eris, which is nearly as large as Pluto, orbits at over twice Pluto's closest approach.
Sending a mission to either of these planets would take decades, and none are in development at the moment, so we can't know what their surfaces look like. But that doesn't mean we know nothing about them. And the James Webb Space Telescope has added to what we know considerably.
The Webb was used to image sunlight reflected off these objects, obtaining its infrared spectrum—the amount of light reflected at different wavelengths. The spectrum is influenced by the chemical composition of the dwarf planets' surfaces. Certain chemicals can absorb specific wavelengths of infrared light, ensuring they don't get reflected. By noting where the spectrum dips, it's possible to figure out which chemicals are present.
Some of that work has already been done. But Webb is able to image parts of the spectrum that were inaccessible earlier, and its instruments are even able to identify different isotopes of the atoms composing each chemical. For example, some molecules of methane (CH4) will, at random, have one of their hydrogen atoms swapped out for its heavier isotope, deuterium, forming CH3D. These isotopes can potentially act as tracers, telling us things about where the chemicals originally came from.
Unexpected findings
Both Eris and Makemake have lots of methane ice on their surfaces, and there are indications of nitrogen ice on Eris, though not Makemake. Strikingly, carbon monoxide appears to be absent from both bodies, even though it's a major component of the ices found on comets, which are also thought to originate in the Kuiper Belt. That's the first hint that something odd might be going on with the surfaces of these bodies.
Also missing is any sign of the more complicated organic molecules that are typically formed when methane is exposed to radiation. These include ethane, ethylene, and acetylene. Water, carbon dioxide, and ammonia also failed to show up in the spectrum.
None of this means these chemicals aren't present on the planets. It just indicates that they're probably not major components of its surface.
The researchers also looked for the presence of methane with different isotopes of its carbon and hydrogen. These include two different versions of carbon (carbon-12 and -13), as well as hydrogen and deuterium. These measurements were converted into ratios between the two isotopes and the ratios compared to those of other bodies in the Solar System.
Bodies that far from the Sun are thought to be composed of materials that have similar isotopic ratios to the raw material that went into building the Solar System since the original isotopes have been frozen in place. Those closer to the Sun are expected to be dynamic enough to undergo chemical reactions that can alter these original ratios. So the results of the Webb imaging seemed strange, as the hydrogen-to-deuterium ratios are much lower than expected for early Solar System material, as registered in a sampling of the comet 67P/Churyumov-Gerasimenko by the Rosetta mission.
By contrast, the ratio between the two different carbon isotopes was about what you'd expect, suggesting that whatever was altering the hydrogen-to-deuterium ratio wasn't simply doing it as a function of isotope weight.
Making sense of it all
So the researchers were left with a number of mysteries. One was the unexpected hydrogen isotopes. Another was the fact that many of the expected ices seemed to be missing in the spectrum. Finally, that much methane on the surface should have reacted to produce more complex organic chemicals, as seen on other bodies of the Solar System. But those were missing as well.
The researchers noted that the hydrogen isotope ratios looked a lot like those from water found in icy bodies throughout the Solar System. So they decided to check whether some of the methane could have been formed sometime after Makemake and Eris.
The idea would involve water either reacting with a simple carbon compound, such as carbon monoxide, to produce methane or participating in the breakdown of more complex organic chemicals. Either would result in methane with a similar isotope ratio to the water that is seen elsewhere in the Solar System. But the reactions that can do so require temperatures significantly above the boiling point of water. That's a bit unexpected for icy bodies like Makemake or Eris, which don't undergo the sort of gravitational interactions that create oceans on moons like Enceladus and Mimas.
But estimates of the radioactive decay in the rocky cores of these bodies would likely create sufficiently high temperatures for a chunk of their history. This is especially true of Eris, which has a high density that suggests a relatively large rocky core. Implicit in this analysis is that the heat was probably sufficient to have created a sub-surface ocean and driven enough circulation in the ices of the crust to have brought the methane formed to the surface.
A striking possibility is that some aspects of this process might still be going on. That would explain the relative absence of complex organic chemicals on the surface of Eris and, to a lesser extent, Makemake (which has a somewhat reddish tint). This could be accounted for if some process were still bringing fresh methane to the surface. It doesn't necessarily involve a sub-surface ocean, but it will involve enough heat to cause parts of the crust to circulate between the surface and the core/crust boundary.
It's important to recognize that this work is built on a number of assumptions and approximations and can't be viewed as the last word on things. The ideas here would benefit from a better sampling of material in comets, which should share a lot of the basic chemistry with these dwarf planets but lack the potential for internal heating.
Still, given what we've learned about Pluto and other icy bodies, the ideas here don't seem as radical as they might have a few decades ago. What does seem radical is our ability to measure isotope ratios in planets that far from Earth.
Quelle: arsTechnica
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Update: 22.02.2024
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James Webb Space Telescope finds neutron star mergers forge gold in the cosmos: 'It was thrilling'
"This is the first time we've been able to verify that metals heavier than iron and silver were freshly made in front of us."
An illustration of two neutron stars colliding and merging to create a kilonova blast. (Image credit: Robin Dienel/Carnegie Institution for Science)
Scientists have analyzed an unusually long blast of high-energy radiation, known as a gamma-ray burst (GRB), and determined that it originated from the collision of two ultradense neutron stars. And, importantly, this result helped the team observe a flash of light emanating from the same event that confirms these mergers are the sites that create elements like gold.
The observations, made using the James Webb Space Telescope (JWST) and the Hubble Space Telescope, allowed scientists to see gold and heavy elements forged, which could help us better understand how these powerful neutron star merger events generate the only environments in the universe turbulent enough to create elements heavier than iron, such as silver and gold which results in a flash of light called a kilonova.
"It was thrilling to study a kilonova as we had never seen before using the powerful eyes of Hubble and JWST," research team member and University of Rome astrophysicist Eleonora Troja told Space.com. "This is the first time we've been able to verify that metals heavier than iron and silver were freshly made in front of us,"
GRBs, which are the most powerful explosions of energy in the known universe, have been associated with neutron star mergers before — but this discovery is different.
These phenomena can be divided into two groups. On one hand, there are the long GRBs that last over 2 seconds and, on the other, short GRBs that last less than 2 seconds. While neutron star mergers have been associated with short GRBs, long GRBs were believed to occur as the result of the collapse of massive stars and not from such collisions.
The extremely bright and long burst, designated GRB 230307A, and detected by devices onboard NASA's Fermi mission in March 2023 lasted 200 seconds; this marked the second most energetic GRB ever seen. It seemed to be associated with a kilonova, designated AT2017gfo, and a neutron star merger that happened some 8.3 million light-years away, breaking the usual GRB convention and challenging theories of how these blasts of high-energy radiation are launched.
"It is challenging to conceive that the duration of GRBs originating from compact binary mergers can extend to tens of seconds," Yu-Han Yang, research team leader and University of Rome postdoctoral astrophysicist, told Space.com.
Gamma-ray discovery could be a cosmic gold-mine
Stars are like stellar furnaces that forge the elements in the periodic table, beginning with the nuclear fusion of hydrogen to helium in their cores and continuing with the fusion of helium to heavier elements like nitrogen, oxygen and carbon.
The most massive stars, around 7 to 8 times as massive as the sun, can forge elements all the way up to iron in their hearts. Once a stellar core is filled with this element, fusion ceases. That also cuts off the outward energy line that had been supporting the star against its own gravity for millions, or sometimes billions, of years. The cores of these massive stars then collapse under this crushing gravity, blowing away their outer layers in supernova explosions.
This collapse transforms the stellar core, crushing electrons and protons into a sea of flowing neutrons, particles found in atomic nuclei that very rarely exist "freely." Yet, in this sea, the neutrons are prevented from squeezing close together by a quantum principle called neutron degeneracy pressure, which can be overcome with enough mass to create a black hole. But sometime there isn't enough mass for a black hole to come into existence.
Those dead stellar cores without the mass to overcome degeneracy pressure are left as 12-mile (20-kilometer) wide bosies with masses between one and two times that of the sun. However, there is a way that neutron stars can contribute heavier elements than iron to the universe.
Not all neutron stars exist alone.
Some traverse the cosmos in neutron star binary systems, meaning they have another neutron star in its gravitational clutches. As these dead stars orbit each other, they set the fabric of space ringing with ripples called gravitational wavesthat gradually carry away angular momentum from the system.
This causes neutron stars to spiral together, emitting gravitational waves faster as time passes and "leaking" more angular momentum in tandem. Ultimately, the two collide and merge. This collision creates a gamma-ray burst and sends out a spray of neutron-rich material that help create the heavier elements of the periodic table.
Other atomic nuclei around these collisions grab the free neutrons via the rapid-neutron capture process, or r-process, and become briefly lived superheavy elements called "lanthanides." Those lanthanides then quickly decay into lighter elements (though elements still heavier than lead.) This decay causes the emission of radiation, light we see from Earth as a "kilonova." Thus, tracking the evolution of kilonovas can help follow the creation of elements like gold and silver.
"Neutron star mergers could give rise to an ideal environment to extensively synthesize heavy elements, which is currently beyond artificial creation," Yang said. "Studying neutron star mergers helps us rewrite the obscure chapters of nucleosynthesis."
Cosmic alchemy in action
Over the course of weeks to months, Yang explained that kilonovas span a wide range of behaviors. These behaviors depend on the composition of the ejected material and the type of remnant formed at the center of the merger site.
Observations of most kilonovas do not extend to such late times in their evolution — but AT2017gfo was different. Unfortunately, however, the late-time observational data for AT2017gfo, collected with the Spitzer Space Telescope, were limited. They only offered weak signals contaminated by the kilonova's host galaxy and presented inadequate coverage in different wavelengths of light.
"During the first few days, the behavior of a kilonova is not affected by its chemical composition," Troja explained. "It takes weeks to reveal which metals are forged in the explosion, and we never had the chance to stare at a kilonova for that long."
These constraints had hindered scientists aiming to understand better kilonovas and the processes that create them.
In the case of AT2017gfo, however, the sensitivity and multi-color coverage of the JWST and Hubble observations allowed Yang and colleagues to observe the luminosity of this kilonova at late times.
"We tracked the evolution of the transient event associated with GRB 230307A up to two months after the burst and captured the full blue-to-red evolution of this transient, which can be classified as a kilonova," Yang said. "We discovered the recession of the photospheric radius at late times. The receding photospheric radius provides evidence for the recombination of heavy elements, such as lanthanides, occurring in the cooling process. Heavy r-process elements are needed to produce the observed data."
This confirmed that neutron star mergers do forge elements heavier than gold, and even confirms that long-GRBs can come from neutron star mergers. It hasn't, thought, solved the mystery of why this particular neutron star merger launched such an unusually long GRB.
"This event proves that a long-duration GRB coming from compact binary mergers is not a fortuitous occurrence," Yang said, adding there are lots of questions to still answer about these events. "What enlightening revelations can late-time observations of kilonovas offer on nucleosynthesis?
"We look forward to joint observations of long-duration gamma-ray bursts, kilonovas and gravitational waves in the future, which will help unveil the mysteries about such outliers."
The team's research was published on Wednesday (Feb. 21) in the journal Nature.
Quelle: SC
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Update: 2.03.2024
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James Webb Space Telescope reveals how stellar blasts of radiation stunt planet birth
"We think that the solar system formed in an environment similar to Orion, so observing systems like d203-506 is a way to travel back in the past."
Hubble image of the Orion Nebula, and a zoom in on the protoplanetary disc d203-506 taken with the James Webb Space Telescope (Image credit: NASA/STScI/Rice Univ./C.O'Dell et al / O. Berné, I. Schrotter, PDRs4All)
Astronomers have used the James Webb Space Telescope to investigate a stellar nursery packed with infant stars in the Orion Nebula. The investigation has helped to uncover the effect that radiation from massive stars has on planet formation.
The Orion Nebula is a massive complex of gas and dust that forms the building blocks of new stars. In fact, it's the nearest star-forming region to Earth. However, this stellar precursor material can also absorb light, acting as a shield for recently born, post-natal stars. That makes it hard for scientists to see those baby stars from our vantage point on Earth. The light the bodies emanate gets effectively hidden. Fortunately, though, the material is less effective at screening low-energy and long-wavelength light: Infrared light.
What this means is the infrared-sensitive, powerful JWST allows astronomers to peer through the Orion Nebula's clouds, even from about 1,400 light-years away. And, with the team's new research, it has honed in on a disk of material called d203-506. This is a disk currently forming planets. After taking a closer look, the researchers found the so-called protoplanetary disk may be unable to form some planets. They speculate this is due to the actions of other stars.
The protoplanetary disk at hand surrounds a small red dwarf star believed to be less than 1 million years old and have, at most, around 10% of the sun's mass. This means the star is relatively young, and relatively cool. Yet, in addition to being only mildly irradiated by its own central star, d203-506 is also bombarded by harsh, high-energy ultraviolet radiation coming from massive young stars in its surroundings.
"Massive stars that are 10 times the size of the sun are 100,000 times more luminous than the sun, and therefore they cast a strong UV radiation on the disks around nearby sun-like stars," Olivier Berné, team leader and a research scientist at the Institut de Recherche en Astrophysique et Planétologie, told space.com. "This radiation heats up the gas, which then escapes from the disk from which planets are expected to form, a process which we call 'photoevaporation.' Therefore, their action can suppress the formation of planets."
Some stars find it harder to shed mass
A main outcome of the team's research was the discovery that whatever planetary system emerges from disk d203-506 will lack an analog for our solar system's largest world, Jupiter.
This is because the intense blasting of UV radiation is likely to suppress the formation of such a gas giant.
"Thanks to observations in the infrared with JWST, we were able to make a measurement of the rate at which the gas escapes," Berné said. "We found that, in d203-506, the disk loses about one Earth mass per year. That is a lot of mass loss!"
This investigation was necessary because, somewhat ironically, massive stars bombarding protoplanetary disks with radiation doesn't always act to suppress planet formation. "We think the solar system formed in an environment similar to Orion, so observing systems like d203-506 is a way to travel back in the past," Berné said.
That, however, raises the question of why the solar system was able to form Jupiter when d203-506 cannot.
"An important parameter is the mass of the star around which planets may form," Berné said. "The star of d203-506 is five to 10 times less massive than the sun. Therefore, it has a weak gravitational field, which means its disk cannot resist photoevaporation well. A star like the sun has a larger gravitational field, so it would be able to better resist photoevaporation."
The protoplanetary disk d203-506 first came to the attention of the team behind this discovery after it was observed with the Hubble Space Telescope and the Atacama Large Millimeter/submillimeter Array (ALMA) in Northern Chile.
"It was a bit serendipitous. This object was seen with Hubble, but it was very faint. In some previous observations with ALMA, however, we saw it was quite bright, so we zoomed in with ALMA. Our ALMA data was also very nice, so we thought we should observe it with JWST," Berné said. "The JWST delivered many surprises, one of the greatest was how rich the spectra we obtained were.
"There is an incredible amount of information in the data; it has already been a year since we obtained it, but we probably used only 10% of the useful information."
The team's research will be published in the March 1 edition of the journal Science.
Quelle: SC