Certain Ultralight-Bosons were expected to slow down the spin of black holes. But new results are contradicting.
For an amateur, many queries would emerge in mind while reading about this kind of intriguing topic. So let’s start from the basics. Almost 85 % of our universe is believed to be filled with unseen matter. But the presence of this anomalous type of matter is evident in various studies. It is called Darkmatter because it doesn’t interact with any type of radiation. Hence it is almost impossible to detect these. This matter is abundant in nature. It is also responsible for the structure and evolution of our universe. With new researches and studies coming up every day, this field of research is becoming more and more exciting. Now let us come to the gist of this article.
What is the connection between Black holes and Dark matter studies?
Is there any connection between Black holes and Dark matter? Before answering the question let’s familiarise ourselves with one more core concept. It links the Black holes and Dark matter. They are the Ultralight bosons, Probably the star of our show 🙂 . These bosons are hypothetical particles that are very light. They are expected to interact less with the surroundings. So, they were avoided from searches till now. A type of ultralight bosons called the axions are almost similar to be a form of dark matter.
Black holes can be used for the search of this type of bosons. Hence the researchers from MIT’s LIGO ( the Laser Interferometer Gravitational-wave Observatory) and its companion detector Virgo observatory started their quest to find these mysterious particles. This research is supported partly by the National Science Foundation. The team includes Salvatore Vitale (Co-Author), Assistant professor of physics at MIT, and lead author Kwan Yeung (Ken) Ng, a graduate student in MIT’s Kavli Institute for Astrophysics and Space Research. The remaining researchers are from Utrecht University in the Netherlands and the Chinese University of Hong Kong. The team published their results in Physical Review Letters. This is the first study to use the spins of black holes detected by LIGO and Virgo’s gravitational-wave data, to look for dark matter .
BLACK HOLES AND ULTRALIGHT BOSONS
According to Vitale “There are different types of bosons, and we have probed one, There may be others, and we can apply this analysis to the growing dataset that LIGO and Virgo will provide over the next few years.”
Black holes are heavy mass objects. Quantum theory predicts that a black hole of a certain mass should pull in clouds of ultralight bosons. This in turn would reduce the speed of the spin of Blackhole than expected spins. So if such types of particles exist the blackholes of a specific mass would have comparatively low spins. These are the hypothesis based on which studies were initiated.
But the results were not so supportive when studies were carried on recently discovered black holes. They were spinning more than the limit expected. Hence the concept of ultralight bosons is ruled out. It further narrows the search for axions and other ultralight bosons. There are two main reasons for narrowing this hypothesis.
SUPER RADIANCE
Using astrophysical and tabletop experiments ultra-light bosons were searched. Using the data , the wide range of possible masses was narrowed down. This was done across a huge range of super-light masses. From 1×10-33 electronvolts to 1×10-6 electronvolts. From the early ’20s, physicists proposed that black holes could be another means of detecting ultralight bosons. Because of an effect called superradiance.
If ultralight bosons exist, they could interact with a black hole under the right circumstances. On the microscopic scale, quantum theory overrules the classical concept. This scale, known as the Compton wavelength, is inversely proportional to the particle mass. Since these ultraviolet bosons are very light their wavelength would be very large. Sometimes this becomes comparable to the limits of a black hole. So superradiance is expected to develop quickly at this time. These bosons are expected to originate from the vacuum around a black hole. These could emerge in large amounts and could collectively drag the blackhole. It will reduce the spin of the black hole itself. And scientists believe that it could occur over several thousand years in astronomical timescales.
“If you jump onto and then down from a carousel, you can steal energy from the carousel,” Vitale says. “These bosons do the same thing to a black hole.” “If bosons exist, we would expect that the old black holes of appropriate mass don’t have large spins. Since the boson clouds would have extracted most of it,” Ng says. “This implies that the discovery of a black hole with large spins can rule out the existence of bosons with certain masses.”
CONTRADICTION IN SPIN VALUE MEASUREMENTS
Measurements were made using LIGO. The previous reasonings were applied by Ng and Vitale to the data obtained. The detectors “listen” for gravitational waves from merging black hole binaries.
The team searched the 45 blackhole binary data reported by VIRGO and LIGO till now. The binaries are very massive, 10 to 70 times our sun. And these indicate that if they had interacted with ultralight bosons, the particles would have different masses.
For each black hole, the team calculated the spin that it should have if the black hole was spun down by ultralight bosons. These bosons are within the corresponding mass range. From their analysis, two black holes stood out: GW190412 and GW190517. But these had spin more than expected topspin at which blackhole can rotate. GW190517 is spinning at close to that maximum. The researchers calculated that if ultralight bosons existed, they would have decreased their spin by a factor of two.
“If they exist, these things would have sucked up a lot of angular momentum,” Vitale says. “They’re really vampires.”
Variations in spin
Now, this is different from our expectations. We expected to find black holes having low spins but we got Blackholes having more spins. Researchers tried to explain possible scenarios for generating the black holes with large spins. Simultaneously allowing for the existence of ultralight bosons. For instance, a black hole could have been spun down by bosons. But then subsequently sped up again through interactions with the surrounding accretion disk. The accretion disk is a disk of matter from which the black hole could suck up energy and momentum.
“If you do the math, you find it takes too long to spin up a black hole to the level that we see here,” Ng says. “So, we can safely ignore this spin-up effect.”
In other words, it’s impossible for the alternate scenario to exist. The black holes’ high spins along with ultralight bosons don’t exist. After the masses and high spins of both black holes were determined. The researchers ruled out the existence of ultralight bosons with masses between 1.3×10-13 electronvolts and 2.7×10-13 electronvolts.
“We’ve basically excluded some type of bosons in this mass range,” Vitale says. “This work also shows how gravitational-wave detections can contribute to searches for elementary particles.”
Reference : MIT News : Black holes and Dark matter
You may also like : A new hunting strategy for dark matter
Author
