Nov 14, 2022 02:06 AM
(This post was last modified: Nov 14, 2022 09:32 AM by C C.)
The Enduring Mystery of the Dragonfly 44 Galaxy
https://www.quantamagazine.org/the-endur...-20221107/
INTRO: In 2016, astronomers led by Pieter van Dokkum of Yale University published a bombshell paper claiming the discovery of a galaxy so dim, yet so broad and heavy, that it must be almost entirely invisible. They estimated that the galaxy, dubbed Dragonfly 44, is 99.99% dark matter.
A heated debate ensued about Dragonfly 44’s properties that remains unresolved. Meanwhile, more than 1,000 similarly big but faint galaxies have turned up.
Dragonfly 44 and its ilk are known as ultra-diffuse galaxies (UDGs). While they can be as large as the largest ordinary galaxies, UDGs are exceptionally dim — so dim that, in telescope surveys of the sky, “it’s a task to filter out the noise without accidentally filtering out these galaxies,” said Paul Bennet, an astronomer at the Space Telescope Science Institute in Baltimore. The bright star-forming gas that’s abundant in other galaxies seems to have vanished in UDGs, leaving only a skeleton of elderly stars.
Their existence has caused a stir in galactic evolutionary theory, which failed to predict them. “They didn’t turn up in simulations,” van Dokkum said. “You have to do something special to make a galaxy that big and faint.”
Wild new theories have emerged to explain how Dragonfly 44 and other UDGs came about. And these giant smudges of light may be providing fresh evidence of dark matter’s invisible hand... (MORE - details)
We need to intercept our next interstellar visitor to see if It's artificial, astronomers say in new study
https://www.vice.com/en/article/wxnbmz/w...-new-study
EXCERPTS: Scientists are gaming out the best way to intercept objects that zoom into our solar system from interstellar space, an effort that could provide close-up views of entities that hail from alien star systems. Sending spacecraft to catch up with these interstellar objects, and potentially capture images of them from distances of just a few hundred miles, could reveal important details about their composition, evolution, and their origin beyond our solar neighborhood, reports a new study.
It’s been only five years since the discovery of the first known interstellar visitor—a mysterious 300-foot-wide object known as ‘Oumuamua—which was spotted traveling through the solar system in October 2017. In addition to its sheer novelty, ‘Oumuamua was something of an oddball that puzzled scientists, especially because it underwent a sudden speed boost that still remains unexplained.
[...] Now, a team led by Amir Siraj, a student pursuing astrophysics at Harvard University, have outlined some of the physical parameters of such a mission, including the potential timeline, spacecraft speed, and optimal distance of a flyby.
[...] The new study also notes that the Vera C. Rubin Telescope’s Legacy Survey of Space and Time (LSST), a huge 10-year astronomical survey, will be an excellent detector for interstellar objects, and could potentially spot dozens of these visitors. An intercept mission would need to rapidly select one of these potentially abundant targets after its detection, then blast off within weeks in order to have enough time to catch up with it.
“If you're going to go after an interstellar object with a billion dollar spacecraft, you probably want it to look a little bit unusual,” Siraj said. “For an ‘Oumuamua-sized object, it's a couple of months for the trip and for an object 10 times dimmer than ‘Oumuamua, meaning a third of the size of ‘Oumuamua, the trip would be a couple of weeks, so you would need to really decide very quickly.”
For this reason, Siraj and his colleagues suggest parking a spacecraft in Lagrange Point 2 (L2), a stable region in space where the James Webb Space Telescope is currently located. From this spot, a spacecraft could swiftly chase after objects that appear interesting at first glance, though the team noted that a mission could also be parked in orbit around Earth or the Moon, or could launch from the ground... (MORE - missing details)
‘Overweight’ neutron star defies a black hole theory, say astronomers
https://www.theguardian.com/science/2022...stronomers
INTRO: An “overweight” neutron star has been observed by astronomers, who say the mysterious object confounds astronomical theories.
The hypermassive star was produced by the merger of two smaller neutron stars. Normally such collisions result in neutron stars so massive that they collapse into a black hole almost instantaneously under their own gravity. But the latest observations revealed the monster star hovering in view for more than a day before it faded out of sight.
“Such a massive neutron star with a long life expectancy is not normally thought to be possible,” said Dr Nuria Jordana-Mitjans, an astronomer at the University of Bath. “It is a mystery why this one was so long-lived.”
The observations also raise questions about the source of incredibly energetic flashes, known as short gamma-ray bursts (GRBs), that accompany neutron star mergers. These outbursts – the most energetic events in the universe since the big bang – were widely assumed to be launched from the poles of the newly formed black hole. But in this case, the observed gamma-ray burst must have emanated from the neutron star itself, suggesting that an entirely different process was at play... (MORE - details)
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Black holes don’t always power gamma-ray bursts, new research shows
https://www.bath.ac.uk/announcements/bla...rch-shows/
RELEASE: Gamma-ray bursts (GRBs) have been detected by satellites orbiting Earth as luminous flashes of the most energetic gamma-ray radiation lasting milliseconds to hundreds of seconds. These catastrophic blasts occur in distant galaxies, billions of light years from Earth.
A sub-type of GRB known as a short-duration GRB starts life when two neutron stars collide. These ultra-dense stars have the mass of our Sun compressed down to half the size of a city like London, and in the final moments of their life, just before triggering a GRB, they generate ripples in space-time -- known to astronomers as gravitational waves.
Until now, space scientists have largely agreed that the 'engine' powering such energetic and short-lived bursts must always come from a newly formed black hole (a region of space-time where gravity is so strong that nothing, not even light, can escape from it). However, new research by an international team of astrophysicists, led by Dr Nuria Jordana-Mitjans at the University of Bath in the UK, is challenging this scientific orthodoxy.
According to the study's findings, some short-duration GRBs are triggered by the birth of a supramassive star (otherwise known as a neutron star remnant) not a black hole.
Dr Jordana-Mitjans said: "Such findings are important as they confirm that newborn neutron stars can power some short-duration GRBs and the bright emissions across the electromagnetic spectrum that have been detected accompanying them. This discovery may offer a new way to locate neutron star mergers, and thus gravitational waves emitters, when we're searching the skies for signals."
Competing theories. Much is known about short-duration GRBs. They start life when two neutron stars, which have been spiralling ever closer, constantly accelerating, finally crash. And from the crash site, a jetted explosion releases the gamma-ray radiation that makes a GRB, followed by a longer-lived afterglow. A day later, the radioactive material that was expelled in all directions during the explosion produces what researchers call a kilonova.
However, precisely what remains after two neutron stars collide -- the 'product' of the crash -- and consequently the power source that gives a GRB its extraordinary energy, has long been a matter of debate. Scientists may now be closer to resolving this debate, thanks to the findings of the Bath-led study.
Space scientists are split between two theories. The first theory has it that neutron stars merge to briefly form an extremely massive neutron star, only for this star to then collapse into a black hole in a fraction of a second. The second argues that the two neutron stars would result in a less heavy neutron star with a higher life expectancy.
So the question that has been needling astrophysicists for decades is this: are short-duration GRBs powered by a black hole or by the birth of a long-lived neutron star?
To date, most astrophysicists have supported the black hole theory, agreeing that to produce a GRB, it is necessary for the massive neutron star to collapse almost instantly.
Electromagnetic signals. Astrophysicists learn about neutron star collisions by measuring the electromagnetic signals of the resultant GRBs. The signal originating from a black hole would be expected to differ from that coming from a neutron star remnant.
The electromagnetic signal from the GRB explored for this study (named GRB 180618A) made it clear to Dr Jordana-Mitjans and her collaborators that a neutron star remnant rather than a black hole must have given rise to this burst.
Elaborating, Dr Jordana-Mitjans said: "For the first time, our observations highlight multiple signals from a surviving neutron star that lived for at least one day after the death of the original neutron star binary."
Professor Carole Mundell, study co-author and professor of Extragalactic Astronomy at Bath, where she holds the Hiroko Sherwin Chair in Extragalactic Astronomy, said: "We were excited to catch the very early optical light from this short gamma-ray burst -- something that is still largely impossible to do without using a robotic telescope. But when we analysed our exquisite data, we were surprised to find we couldn't explain it with the standard fast-collapse black hole model of GRBs.
"Our discovery opens new hope for upcoming sky surveys with telescopes such as the Rubin Observatory LSST with which we may find signals from hundreds of thousands of such long-lived neutron stars, before they collapse to become black holes."
Disappearing afterglow. What initially puzzled the researchers was that the optical light from the afterglow that followed GRB 180618A disappeared after just 35 minutes. Further analysis showed that the material responsible for such a brief emission was expanding close to the speed of light due to some source of continuous energy that was pushing it from behind.
What was more surprising was that this emission had the imprint of a newborn, rapidly spinning and highly magnetised neutron star, called a millisecond magnetar. The team found that the magnetar after GRB 180618A was reheating the leftover material of the crash as it was slowing down.
In GRB 180618A, the magnetar-powered optical emission was one-thousand times brighter than what was expected from a classical kilonova.
https://www.quantamagazine.org/the-endur...-20221107/
INTRO: In 2016, astronomers led by Pieter van Dokkum of Yale University published a bombshell paper claiming the discovery of a galaxy so dim, yet so broad and heavy, that it must be almost entirely invisible. They estimated that the galaxy, dubbed Dragonfly 44, is 99.99% dark matter.
A heated debate ensued about Dragonfly 44’s properties that remains unresolved. Meanwhile, more than 1,000 similarly big but faint galaxies have turned up.
Dragonfly 44 and its ilk are known as ultra-diffuse galaxies (UDGs). While they can be as large as the largest ordinary galaxies, UDGs are exceptionally dim — so dim that, in telescope surveys of the sky, “it’s a task to filter out the noise without accidentally filtering out these galaxies,” said Paul Bennet, an astronomer at the Space Telescope Science Institute in Baltimore. The bright star-forming gas that’s abundant in other galaxies seems to have vanished in UDGs, leaving only a skeleton of elderly stars.
Their existence has caused a stir in galactic evolutionary theory, which failed to predict them. “They didn’t turn up in simulations,” van Dokkum said. “You have to do something special to make a galaxy that big and faint.”
Wild new theories have emerged to explain how Dragonfly 44 and other UDGs came about. And these giant smudges of light may be providing fresh evidence of dark matter’s invisible hand... (MORE - details)
We need to intercept our next interstellar visitor to see if It's artificial, astronomers say in new study
https://www.vice.com/en/article/wxnbmz/w...-new-study
EXCERPTS: Scientists are gaming out the best way to intercept objects that zoom into our solar system from interstellar space, an effort that could provide close-up views of entities that hail from alien star systems. Sending spacecraft to catch up with these interstellar objects, and potentially capture images of them from distances of just a few hundred miles, could reveal important details about their composition, evolution, and their origin beyond our solar neighborhood, reports a new study.
It’s been only five years since the discovery of the first known interstellar visitor—a mysterious 300-foot-wide object known as ‘Oumuamua—which was spotted traveling through the solar system in October 2017. In addition to its sheer novelty, ‘Oumuamua was something of an oddball that puzzled scientists, especially because it underwent a sudden speed boost that still remains unexplained.
[...] Now, a team led by Amir Siraj, a student pursuing astrophysics at Harvard University, have outlined some of the physical parameters of such a mission, including the potential timeline, spacecraft speed, and optimal distance of a flyby.
[...] The new study also notes that the Vera C. Rubin Telescope’s Legacy Survey of Space and Time (LSST), a huge 10-year astronomical survey, will be an excellent detector for interstellar objects, and could potentially spot dozens of these visitors. An intercept mission would need to rapidly select one of these potentially abundant targets after its detection, then blast off within weeks in order to have enough time to catch up with it.
“If you're going to go after an interstellar object with a billion dollar spacecraft, you probably want it to look a little bit unusual,” Siraj said. “For an ‘Oumuamua-sized object, it's a couple of months for the trip and for an object 10 times dimmer than ‘Oumuamua, meaning a third of the size of ‘Oumuamua, the trip would be a couple of weeks, so you would need to really decide very quickly.”
For this reason, Siraj and his colleagues suggest parking a spacecraft in Lagrange Point 2 (L2), a stable region in space where the James Webb Space Telescope is currently located. From this spot, a spacecraft could swiftly chase after objects that appear interesting at first glance, though the team noted that a mission could also be parked in orbit around Earth or the Moon, or could launch from the ground... (MORE - missing details)
‘Overweight’ neutron star defies a black hole theory, say astronomers
https://www.theguardian.com/science/2022...stronomers
INTRO: An “overweight” neutron star has been observed by astronomers, who say the mysterious object confounds astronomical theories.
The hypermassive star was produced by the merger of two smaller neutron stars. Normally such collisions result in neutron stars so massive that they collapse into a black hole almost instantaneously under their own gravity. But the latest observations revealed the monster star hovering in view for more than a day before it faded out of sight.
“Such a massive neutron star with a long life expectancy is not normally thought to be possible,” said Dr Nuria Jordana-Mitjans, an astronomer at the University of Bath. “It is a mystery why this one was so long-lived.”
The observations also raise questions about the source of incredibly energetic flashes, known as short gamma-ray bursts (GRBs), that accompany neutron star mergers. These outbursts – the most energetic events in the universe since the big bang – were widely assumed to be launched from the poles of the newly formed black hole. But in this case, the observed gamma-ray burst must have emanated from the neutron star itself, suggesting that an entirely different process was at play... (MORE - details)
- - - - - - - - -
Black holes don’t always power gamma-ray bursts, new research shows
https://www.bath.ac.uk/announcements/bla...rch-shows/
RELEASE: Gamma-ray bursts (GRBs) have been detected by satellites orbiting Earth as luminous flashes of the most energetic gamma-ray radiation lasting milliseconds to hundreds of seconds. These catastrophic blasts occur in distant galaxies, billions of light years from Earth.
A sub-type of GRB known as a short-duration GRB starts life when two neutron stars collide. These ultra-dense stars have the mass of our Sun compressed down to half the size of a city like London, and in the final moments of their life, just before triggering a GRB, they generate ripples in space-time -- known to astronomers as gravitational waves.
Until now, space scientists have largely agreed that the 'engine' powering such energetic and short-lived bursts must always come from a newly formed black hole (a region of space-time where gravity is so strong that nothing, not even light, can escape from it). However, new research by an international team of astrophysicists, led by Dr Nuria Jordana-Mitjans at the University of Bath in the UK, is challenging this scientific orthodoxy.
According to the study's findings, some short-duration GRBs are triggered by the birth of a supramassive star (otherwise known as a neutron star remnant) not a black hole.
Dr Jordana-Mitjans said: "Such findings are important as they confirm that newborn neutron stars can power some short-duration GRBs and the bright emissions across the electromagnetic spectrum that have been detected accompanying them. This discovery may offer a new way to locate neutron star mergers, and thus gravitational waves emitters, when we're searching the skies for signals."
Competing theories. Much is known about short-duration GRBs. They start life when two neutron stars, which have been spiralling ever closer, constantly accelerating, finally crash. And from the crash site, a jetted explosion releases the gamma-ray radiation that makes a GRB, followed by a longer-lived afterglow. A day later, the radioactive material that was expelled in all directions during the explosion produces what researchers call a kilonova.
However, precisely what remains after two neutron stars collide -- the 'product' of the crash -- and consequently the power source that gives a GRB its extraordinary energy, has long been a matter of debate. Scientists may now be closer to resolving this debate, thanks to the findings of the Bath-led study.
Space scientists are split between two theories. The first theory has it that neutron stars merge to briefly form an extremely massive neutron star, only for this star to then collapse into a black hole in a fraction of a second. The second argues that the two neutron stars would result in a less heavy neutron star with a higher life expectancy.
So the question that has been needling astrophysicists for decades is this: are short-duration GRBs powered by a black hole or by the birth of a long-lived neutron star?
To date, most astrophysicists have supported the black hole theory, agreeing that to produce a GRB, it is necessary for the massive neutron star to collapse almost instantly.
Electromagnetic signals. Astrophysicists learn about neutron star collisions by measuring the electromagnetic signals of the resultant GRBs. The signal originating from a black hole would be expected to differ from that coming from a neutron star remnant.
The electromagnetic signal from the GRB explored for this study (named GRB 180618A) made it clear to Dr Jordana-Mitjans and her collaborators that a neutron star remnant rather than a black hole must have given rise to this burst.
Elaborating, Dr Jordana-Mitjans said: "For the first time, our observations highlight multiple signals from a surviving neutron star that lived for at least one day after the death of the original neutron star binary."
Professor Carole Mundell, study co-author and professor of Extragalactic Astronomy at Bath, where she holds the Hiroko Sherwin Chair in Extragalactic Astronomy, said: "We were excited to catch the very early optical light from this short gamma-ray burst -- something that is still largely impossible to do without using a robotic telescope. But when we analysed our exquisite data, we were surprised to find we couldn't explain it with the standard fast-collapse black hole model of GRBs.
"Our discovery opens new hope for upcoming sky surveys with telescopes such as the Rubin Observatory LSST with which we may find signals from hundreds of thousands of such long-lived neutron stars, before they collapse to become black holes."
Disappearing afterglow. What initially puzzled the researchers was that the optical light from the afterglow that followed GRB 180618A disappeared after just 35 minutes. Further analysis showed that the material responsible for such a brief emission was expanding close to the speed of light due to some source of continuous energy that was pushing it from behind.
What was more surprising was that this emission had the imprint of a newborn, rapidly spinning and highly magnetised neutron star, called a millisecond magnetar. The team found that the magnetar after GRB 180618A was reheating the leftover material of the crash as it was slowing down.
In GRB 180618A, the magnetar-powered optical emission was one-thousand times brighter than what was expected from a classical kilonova.
