Mar 20, 2025 06:08 PM
(This post was last modified: Mar 21, 2025 04:48 PM by C C.)
How black holes could nurture life
https://www.eurekalert.org/news-releases/1077663
INTRO: At the center of most large galaxies, including our own Milky Way, sits a supermassive black hole. Interstellar gas periodically falls into the orbit of these bottomless pits, switching the black hole into active galactic nucleus (AGN)-mode, blasting high-energy radiation across the galaxy.
It's not an environment you'd expect a plant or animal to thrive in. But in a surprising new study in the Astrophysical Journal, researchers at Dartmouth and the University of Exeter show that AGN radiation can have a paradoxically nurturing effect on life. Rather than doom a species to oblivion, it can help ensure its success.
The study may be the first to concretely measure, via computer simulations, how an AGN's ultraviolet radiation can transform a planet's atmosphere to help or hinder life. Consistent with studies looking at the effects of solar radiation, the researchers found that the benefits—or harms—depend on how close the planet is to the source of the radiation, and whether life has already gained a toehold.
"Once life exists, and has oxygenated the atmosphere, the radiation becomes less devastating and possibly even a good thing," says the study's lead author, Kendall Sippy, who graduated from Dartmouth last year. "Once that bridge is crossed, the planet becomes more resilient to UV radiation and protected from potential extinction events."
The researchers simulated the effects of AGN radiation on not only Earth, but Earth-like planets of varying atmospheric composition. If oxygen was already present, they found, the radiation would set off chemical reactions causing the planet's protective ozone layer to grow. The more oxygenated the atmosphere, the greater the effect.
High-energy light reacts readily with oxygen, splitting the molecule into single atoms that recombine to form ozone. As ozone builds up in the upper atmosphere, it deflects more and more dangerous radiation back into space. Earth owes its favorable climate to a similar process that happened about 2 billion years ago with the first oxygen-producing microbes.
Radiation from the sun helped Earth's fledgling life oxygenate, and add ozone, to the atmosphere. As our planet's protective ozone blanket thickened, it allowed life to flourish, producing more oxygen, and yet more ozone. Under the Gaia hypothesis, these beneficial feedback loops allowed complex life to emerge.
"If life can quickly oxygenate a planet's atmosphere, ozone can help regulate the atmosphere to favor the conditions life needs to grow," says study co-author Jake Eager-Nash, a postdoctoral fellow at the University of Victoria. "Without a climate-regulating feedback mechanisms, life may die out fast."
Earth, in real life, is not close enough to its resident black hole, Sagittarius A, to feel its effects, even in AGN-mode. But the researchers wanted to see what could happen if Earth were much closer to a hypothetical AGN, and thus exposed to radiation billions of times greater.
Recreating Earth's oxygen-free atmosphere in the Archean, they found that the radiation would all but preclude life from developing. But as oxygen levels rose, nearing modern levels, Earth's ozone layer would grow and shield the ground below from dangerous radiation.
"With modern oxygen levels, this would take a few days, which would hopefully mean that life could survive," Eager-Nash says. "We were surprised by how quickly ozone levels would respond."
When they looked at what could happen on an Earth-like planet in an older galaxy with stars clustered closer to its AGN, they found a much different picture. In a "red nugget relic" galaxy like NGC 1277, the effects would be lethal. Stars in more massive galaxies with an elliptical shape, like Messier-87, or our spiral Milky Way, are spread out more, and thus, farther from an AGN's dangerous radiation... (MORE - details, no ads)
Is dark energy getting weaker? New evidence strengthens the case.
https://www.quantamagazine.org/is-dark-e...-20250319/
INTRO: Last spring, a team of nearly 1,000 cosmologists announced that dark energy — the enigmatic agent propelling the universe to swell in size at an ever-increasing rate — might be slackening. The bombshell result, based on the team’s observations of the motions of millions of galaxies combined with other data, was tentative and preliminary. Today, the scientists report that they have analyzed more than twice as much data as before and that it points more strongly to the same conclusion: Dark energy is losing steam.
“We are much more certain than last year that this is definitely a thing,” said Seshadri Nadathur, a member of the Dark Energy Spectroscopic Instrument (DESI) collaboration, the group behind the new result.
Their finding, presented today at the Global Physics Summit in Anaheim, California, aligns with that of a second group of cosmologists, the 400-strong Dark Energy Survey (DES). Having also observed a huge swath of the cosmos, DES reported evidence of varying dark energy in a paper earlier this month and in a talk today at the Anaheim meeting.
“It’s interesting that things are pushing in this direction and that multiple experiments are seeing some tension” with the idea that dark energy is constant, said Michael Troxel, a member of the DES team based at Duke University.
If the evidence of evolving dark energy holds up as more data accrues — and this is not guaranteed — it would upend cosmologists’ understanding of our ultimate destiny. Dark energy that has a constant density and pressure would doom our cosmos to expand for all time until unbridgeable gulfs separate every particle from all the others, snuffing out all activity. But dark energy that evolves makes alternative futures possible. “It challenges the fate of the universe,” said Mustapha Ishak-Boushaki, a cosmologist at the University of Texas at Dallas and DESI team member. “It’s game-changing.”
Evolving or weakening dark energy would also rewrite our picture of present-day reality. The most straightforward idea is that dark energy is the energy of the vacuum of space itself, which should be an unchanging feature of quantum physics. Evolving dark energy would herald the presence of something extra, some previously undetected ingredient in the fundamental recipe of the cosmos. The missing part could be as simple as a new type of particle, or it could reveal a subtle failure of Einstein’s theory of gravity. It might even lead researchers down a path that ends at a new fundamental theory of physics.
“It sounds like it will be a paradigm shift, something that will change our understanding and the way we are putting all the pieces together,” Ishak-Boushaki said... (MORE - details)
https://www.eurekalert.org/news-releases/1077663
INTRO: At the center of most large galaxies, including our own Milky Way, sits a supermassive black hole. Interstellar gas periodically falls into the orbit of these bottomless pits, switching the black hole into active galactic nucleus (AGN)-mode, blasting high-energy radiation across the galaxy.
It's not an environment you'd expect a plant or animal to thrive in. But in a surprising new study in the Astrophysical Journal, researchers at Dartmouth and the University of Exeter show that AGN radiation can have a paradoxically nurturing effect on life. Rather than doom a species to oblivion, it can help ensure its success.
The study may be the first to concretely measure, via computer simulations, how an AGN's ultraviolet radiation can transform a planet's atmosphere to help or hinder life. Consistent with studies looking at the effects of solar radiation, the researchers found that the benefits—or harms—depend on how close the planet is to the source of the radiation, and whether life has already gained a toehold.
"Once life exists, and has oxygenated the atmosphere, the radiation becomes less devastating and possibly even a good thing," says the study's lead author, Kendall Sippy, who graduated from Dartmouth last year. "Once that bridge is crossed, the planet becomes more resilient to UV radiation and protected from potential extinction events."
The researchers simulated the effects of AGN radiation on not only Earth, but Earth-like planets of varying atmospheric composition. If oxygen was already present, they found, the radiation would set off chemical reactions causing the planet's protective ozone layer to grow. The more oxygenated the atmosphere, the greater the effect.
High-energy light reacts readily with oxygen, splitting the molecule into single atoms that recombine to form ozone. As ozone builds up in the upper atmosphere, it deflects more and more dangerous radiation back into space. Earth owes its favorable climate to a similar process that happened about 2 billion years ago with the first oxygen-producing microbes.
Radiation from the sun helped Earth's fledgling life oxygenate, and add ozone, to the atmosphere. As our planet's protective ozone blanket thickened, it allowed life to flourish, producing more oxygen, and yet more ozone. Under the Gaia hypothesis, these beneficial feedback loops allowed complex life to emerge.
"If life can quickly oxygenate a planet's atmosphere, ozone can help regulate the atmosphere to favor the conditions life needs to grow," says study co-author Jake Eager-Nash, a postdoctoral fellow at the University of Victoria. "Without a climate-regulating feedback mechanisms, life may die out fast."
Earth, in real life, is not close enough to its resident black hole, Sagittarius A, to feel its effects, even in AGN-mode. But the researchers wanted to see what could happen if Earth were much closer to a hypothetical AGN, and thus exposed to radiation billions of times greater.
Recreating Earth's oxygen-free atmosphere in the Archean, they found that the radiation would all but preclude life from developing. But as oxygen levels rose, nearing modern levels, Earth's ozone layer would grow and shield the ground below from dangerous radiation.
"With modern oxygen levels, this would take a few days, which would hopefully mean that life could survive," Eager-Nash says. "We were surprised by how quickly ozone levels would respond."
When they looked at what could happen on an Earth-like planet in an older galaxy with stars clustered closer to its AGN, they found a much different picture. In a "red nugget relic" galaxy like NGC 1277, the effects would be lethal. Stars in more massive galaxies with an elliptical shape, like Messier-87, or our spiral Milky Way, are spread out more, and thus, farther from an AGN's dangerous radiation... (MORE - details, no ads)
Is dark energy getting weaker? New evidence strengthens the case.
https://www.quantamagazine.org/is-dark-e...-20250319/
INTRO: Last spring, a team of nearly 1,000 cosmologists announced that dark energy — the enigmatic agent propelling the universe to swell in size at an ever-increasing rate — might be slackening. The bombshell result, based on the team’s observations of the motions of millions of galaxies combined with other data, was tentative and preliminary. Today, the scientists report that they have analyzed more than twice as much data as before and that it points more strongly to the same conclusion: Dark energy is losing steam.
“We are much more certain than last year that this is definitely a thing,” said Seshadri Nadathur, a member of the Dark Energy Spectroscopic Instrument (DESI) collaboration, the group behind the new result.
Their finding, presented today at the Global Physics Summit in Anaheim, California, aligns with that of a second group of cosmologists, the 400-strong Dark Energy Survey (DES). Having also observed a huge swath of the cosmos, DES reported evidence of varying dark energy in a paper earlier this month and in a talk today at the Anaheim meeting.
“It’s interesting that things are pushing in this direction and that multiple experiments are seeing some tension” with the idea that dark energy is constant, said Michael Troxel, a member of the DES team based at Duke University.
If the evidence of evolving dark energy holds up as more data accrues — and this is not guaranteed — it would upend cosmologists’ understanding of our ultimate destiny. Dark energy that has a constant density and pressure would doom our cosmos to expand for all time until unbridgeable gulfs separate every particle from all the others, snuffing out all activity. But dark energy that evolves makes alternative futures possible. “It challenges the fate of the universe,” said Mustapha Ishak-Boushaki, a cosmologist at the University of Texas at Dallas and DESI team member. “It’s game-changing.”
Evolving or weakening dark energy would also rewrite our picture of present-day reality. The most straightforward idea is that dark energy is the energy of the vacuum of space itself, which should be an unchanging feature of quantum physics. Evolving dark energy would herald the presence of something extra, some previously undetected ingredient in the fundamental recipe of the cosmos. The missing part could be as simple as a new type of particle, or it could reveal a subtle failure of Einstein’s theory of gravity. It might even lead researchers down a path that ends at a new fundamental theory of physics.
“It sounds like it will be a paradigm shift, something that will change our understanding and the way we are putting all the pieces together,” Ishak-Boushaki said... (MORE - details)
