A stunning new image from the South African MeerKAT telescope captures powerful radio emissions woven through space.
The radio emissions emanate from an enormous rotating black hole that lies at the center of an elliptical galaxy known as IC 4296. Energy released by matter falling into the black hole generates two radio jets of high energy gas on opposite sides of the galaxy — creating what is also known as a double-lobed radio galaxy.
The catastrophic blast was 10 times stronger and brighter than a typical supernova.
The blast was 10 times stronger and brighter than a typical supernova, and we can still see its impact today.
The size of a tennis ball. The mass of the Earth.
But that could change soon.
Current gravitational wave observatories are sensitive to the mergers of stellar-mass black holes. We’ve observed a few mergers involving neutron stars, but most have been between black holes on the order of tens of solar masses.
We can’t yet observe the gravitational waves of supermassive black holes in other galaxies, nor can we observe those of planet-sized worlds. Proposed detectors such as eLISA will allow us to observe the former, but it will take a novel new idea to detect the latter.
Posted in cosmology, mathematics, neuroscience
Math about black holes:
If you’ve been following the arXiv, or keeping abreast of developments in high-energy theory more broadly, you may have noticed that the longstanding black hole information paradox seems to have entered a new phase, instigated by a pair of papers [1, 2] that appeared simultaneously in the summer of 2019. Over 200 subsequent papers have since appeared on the subject of “islands”—subleading saddles in the gravitational path integral that enable one to compute the Page curve, the signature of unitary black hole evaporation. Due to my skepticism towards certain aspects of these constructions (which I’ll come to below), my brain has largely rebelled against boarding this particular hype train. However, I was recently asked to explain them at the HET group seminar here at Nordita, which provided the opportunity (read: forced me) to prepare a general overview of what it’s all about. Given the wide interest and positive response to the talk, I’ve converted it into the present post to make it publicly available.
Well, most of it: during the talk I spent some time introducing black hole thermodynamics and the information paradox. Since I’ve written about these topics at length already, I’ll simply refer you to those posts for more background information. If you’re not already familiar with firewalls, I suggest reading them first before continuing. It’s ok, I’ll wait.
Done? Great; let me summarize the pre-island state of affairs with the following two images, which I took from the post-island review [3] (also worth a read):
A new analysis of black hole vibrational spectra identifies which frequencies are stable to perturbations—information pertinent for gravitational-wave analysis and quantum gravity modeling.
Are black holes stable when they are slightly perturbed? This question was answered 50 years ago by the physicist C. V. Vishveshwara with a numerical experiment: Vishveshwara imagined sending a wave packet toward a black hole and observing what came out [1]. He found that the scattered wave is a sum of damped sinusoids, whose frequencies and damping times are the free-vibration modes, or so-called quasinormal modes, of the black hole. The damping implies that black holes are stable—they settle back into a stationary state after being perturbed.
Circa 2020
According to the many-worlds interpretation of quantum mechanics, the universe is constantly dividing and taking you with it – so would you recognise your other selves if you met them?
Another missing piece has just been added to our knowledge of cosmic phenomena. The LIGO, Virgo and KAGRA collaborations have announced the first detection of gravitational waves[1] resulting from the ‘mixed’ merger between a black hole and a neutron star.[2] The discovery, published on June 29, 2021 in Astrophysical Journal Letters, involves CNRS researchers working within the Virgo scientific collaboration.
Although it has only been only a few years since the very first observation of gravitational waves, the technique has yielded an extensive repertoire of phenomena involving massive cosmic objects. The LIGO and Virgo detectors have already observed mergers of pairs (or binaries) of black holes and, less frequently, of neutron stars. However, gravitational waves detected in January 2020 provide evidence of the existence of a new type of system. The signals, named GW200105 and GW200115 from their dates of detection, were produced by a process that had been predicted but never observed until now: the coalescence of ‘mixed pairs’ called NSBH pairs, each made up of a neutron star and a black hole.[3]
Gravitational waves contain valuable information about their source, such as the mass of the components making up the binary. Analysis of the signals revealed that GW200105 resulted from the merger, some 900 million years ago, of a black hole and a neutron star, respectively 8.9 times and 1.9 times more massive than the Sun, while GW200115 originated from an NSBH pair which coalesced around 1 billion years ago, with masses 5.7 and 1.5 times greater than the Sun. The difference in mass between the components of the system indicates that they are indeed mixed binaries: the mass of the heavier object corresponds to that of a black hole while the mass of the lighter object is consistent with that of a neutron star. The difference between the two masses could also explain why no light signals were detected by telescopes. When a neutron star approaches a black hole it can theoretically be torn apart by tidal forces, causing flares of electromagnetic radiation. However, in the two cases observed, the black hole, being much more massive, could have gobbled up the neutron star in a single mouthful, leaving no trace.
The most mysterious objects in space are slowly coming into view.
As we learn more about black holes, we’re able to prove, disprove, or revise old theories. Some big ones, like the information paradox, are coming into view.
Black holes seem like the perfect spot for harvesting energy.
Researchers create a device to test a 50-year-old physics theory from the famed Roger Penrose.
Posted in cosmology
Dark matter could be even weirder than anyone thought, say cosmologists who are suggesting this mysterious substance that accounts for more than 80% of the universe’s mass could interact with itself.
“We live in an ocean of dark matter, yet we know very little about what it could be,” Flip Tanedo, an assistant professor of physics and astronomy at the University of California Riverside, said in a statement.
