Astrophysicists Detect First Black Hole-neutron Star Mergers

Astrophysicists detect first black hole-neutron star mergers

A long time ago, in two galaxies about 900 million light-years away, two black holes each gobbled up their neutron star companions, triggering gravitational waves that finally hit Earth in January 2020.

Discovered by an international team of astrophysicists including Northwestern University researchers, two events—detected just 10 days apart—mark the first-ever detection of a black hole merging with a neutron star. The findings will enable researchers to draw the first conclusions about the origins of these rare binary systems and how often they merge.

“Gravitational waves have allowed us to detect collisions of pairs of black holes and pairs of neutron stars, but the mixed collision of a black hole with a neutron star has been the elusive missing piece of the family picture of compact object mergers,” said Chase Kimball, a Northwestern graduate student who co-authored the study. “Completing this picture is crucial to constraining the host of astrophysical models of compact object formation and binary evolution. Inherent to these models are their predictions of the rates that black holes and neutron stars merge amongst themselves. With these detections, we finally have measurements of the merger rates across all three categories of compact binary mergers.”

The research will be published June 29 in the Astrophysical Journal Letters. The team includes researchers from the LIGO Scientific Collaboration (LSC), the Virgo Collaboration and the Kamioka Gravitational Wave Detector (KAGRA) project. An LSC member, Kimball led calculations of the merger rate estimates and how they fit into predictions from the various formation channels of neutron stars and black holes. He also contributed to discussions about the astrophysical implications of the discovery.

Kimball is co-advised by Vicky Kalogera, the principal investigator of Northwestern’s LSC group, director of the Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) and the Daniel I. Linzer Distinguished Professor of Physics and Astronomy in the Weinberg Colleges of Arts and Sciences; and by Christopher Berry, an LSC member and the CIERA Board of Visitors Research Professor at Northwestern as well as a lecturer at the Institute for Gravitational Research at the University of Glasgow. Other Northwestern co-authors include Maya Fishbach, a NASA Einstein Postdoctoral Fellow and LSC member.

Two events in ten days

The team observed the two new gravitational-wave events—dubbed GW200105 and GW200115—on Jan. 5, 2020, and Jan. 15, 2020, during the second half of the LIGO and Virgo detectors third observing run, called O3b.

Although multiple observatories carried out several follow-up observations, none observed light from either event, consistent with the measured masses and distances.

“Following the tantalizing discovery, announced in June 2020, of a black-hole merger with a mystery object, which may be the most massive neutron star known, it is exciting also to have the detection of clearly identified mixed mergers, as predicted by our theoretical models for decades now,” Kalogera said. “Quantitatively matching the rate constraints and properties for all three population types will be a powerful way to answer the foundational questions of origins.”

All three large detectors (both LIGO instruments and the Virgo instrument) detected GW200115, which resulted from the merger of a 6-solar mass black hole with a 1.5-solar mass neutron star, roughly 1 billion light-years from Earth. With observations of the three widely separated detectors on Earth, the direction to the waves’ origin can be determined to a part of the sky equivalent to the area covered by 2,900 full moons.

Just 10 days earlier, LIGO detected a strong signal from GW200105, using just one detector while the other was temporarily offline. While Virgo also was observing, the signal was too quiet in its data for Virgo to help detect it. From the gravitational waves, the astronomers inferred that the signal was caused by a 9-solar mass black hole colliding with a 1.9-solar mass compact object, which they ultimately concluded was a neutron star. This merger happened at a distance of about 900 million light-years from Earth.

Because the signal was strong in only one detector, the astronomers could not precisely determine the direction of the waves’ origin. Although the signal was too quiet for Virgo to confirm its detection, its data did help narrow down the source’s potential location to about 17% of the entire sky, which is equivalent to the area covered by 34,000 full moons.

Where do they come from?

Because the two events are the first confident observations of gravitational waves from black holes merging with neutron stars, the researchers now can estimate how often such events happen in the universe. Although not all events are detectable, the researchers expect roughly one such merger per month happens within a distance of one billion light-years.

While it is unclear where these binary systems form, astronomers identified three likely cosmic origins: stellar binary systems, dense stellar environments including young star clusters, and the centers of galaxies.

The team is currently preparing the detectors for a fourth observation run, to begin in summer 2022.

“We’ve now seen the first examples of black holes merging with neutron stars, so we know that they’re out there,” Fishbach said. “But there’s still so much we don’t know about neutron stars and black holes—how small or big they can get, how fast they can spin, how they pair off into merger partners. With future gravitational wave data, we will have the statistics to answer these questions, and ultimately learn how the most extreme objects in our universe are made.”

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physicla

3 years ago

hi friends! february has felt like three years and i am glad to see it end. this month was tough for so many different reasons but I'm trying to stay positive. i'm still incredibly intimidated and scared by my course load but I've started properly studying now and feel confident in my ability to at least try. next saturday i'm having lunch with an old friend from secondary school and i'm grateful i have that to look forward to 😊

i hope you're all doing well!

February Productivity Challenge

Day 24: What's your favourite beverage?

Iced coffee made right

Day 25: What does your ideal breakfast look like?

Okay i have two answers for this:

- A smoothie bowl

- Crepes with a tiny amount of syrup, bananas and tea

Day 26: What's the cosiest place in your mind right now?

my bed at like 2 am with the lights off and the window open, covered in blankets with music playing on low (everybody else in the house is asleep)

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physicla

3 years ago

Vera Rubin

Vera Florence Cooper Rubin was an American astronomer who pioneered work on galaxy rotation rates. She uncovered the discrepancy between the predicted angular motion of galaxies and the observed motion, by studying galactic rotation curves. This phenomenon became known as the galaxy rotation problem, and was evidence of the existence of dark matter. Although initially met with skepticism, Rubin’s results were confirmed over subsequent decades. Her legacy was described by The New York Times as “ushering in a Copernican-scale change” in cosmological theory.

Rubin spent her life advocating for women in science and was known for her mentorship of aspiring women astronomers. Her data provided some of the first evidence for dark matter, which had been theorized by Fritz Zwicky in the 1930s. She was honored throughout her career for her achievements, and received the Bruce Medal, the Gold Medal of the Royal Astronomical Society, and the National Medal of Science, among others. source

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physicla

3 years ago

First year physics undergrad recap

I started studying physics one year ago and my blog still lacks activity - thus it’s time to do a recap of my experiences and give you, the new freshmen, some hints!

To be honest despair was my constant companion during the first semester. In the beginning confusion is ominpresent because you have to learn an immense amount of new mathematical stuff you have never imagined before. But as time is passing you get used to it and you start understanding the connections between the topics. The most important advice is to keep going, no matter how frustrated you might be.

In my case I did earnestly not believe to pass any exams for the first months of uni. Each single day showed me how much I did not understand. In retrospect I realize that this feeling is absolutely normal - your endurance is being tested. Gladly I did never resign and kept on learning. As a result free time was not really existent during these months. But this proved to be worthwile - I passed all exams and with some luck I finished the first semester even with good grades.

At LMU Munich you have three lectures in the first semester: E1 (experimental physics - classical mechanics), M1 (mathematics for physisicsts - calculus) and T0 (mathematical methods for theoretical physics). At least E1 sometimes resembles the physics you are used to. There the math is not as heavy as the stuff you need to use later. But you learn all of this heavy math in T0 - the most challenging lecture as I experienced it. And well yeah - calculus was just a bunch of confusion for me. To prove Lemmas, Propositions etc. in correct mathematical language was something absolutely new. To calculate and to prove are completely different things - but you can get used to it, even if it takes a lot of time! Practice makes perfect.

Luckily the second semester was way better than the first. I proved to myself that I can make this and got a higher frustration tolerance. I believe that most of the students feel this way. The lectures then were E2 (experimental physics - thermodynamics and electrodynamics), T1 (theoretical physics - classical mechanics) and M2 (mathematics for physicists - linear algebra). Though it is still damn difficult, your fundament of knowledge you earned during the first semester helps you everyday. Still you won’t be safe from failing exams - I did not pass linear algebra this semester. About 80% didn’t. But I have a lot of hope for the retry exam - It’s okay to fail sometimes. [Edit: I actually passed it, yay!]

Now let’s give you some tips for your first months as a freshman!

Go to each lecture and tutorial

The moment you start not going to lectures is a dangerous step. In some cases (if the professor gives an absolutely terrible lecture) it might make sense. But not going to uni because of despair and resignation is the worst thing you can do. Once you started this it becomes a vicious circle. It’s way more difficult to learn absolutely everything by yourself. It’s really helpful to get a better start into new topics with attending lectures. Otherwise it gets more difficult than it is anyway and you lose motivation more and more.

Get used to work by yourself

Try to get a balance between discussing with others and solving problems on your own. Both extremes do not ensure effective learning. You need to ponder by yourself. But when you’re struck for hours, you should get help - discussing is important, even if you do not get the right results.

Do not let bad habits overwhelm you

Going to uni everyday for often more than eight hours can lead to very unhealthy habits, such as not eating the whole day, not making real breaks because you’re under pressure, smoking a lot, etc. At least these had been my problems. Maybe I have the tendency for bad habits anyway :D I think it’s still important to say: Don’t forget to eat, drink and take breaks - otherwise your brain won’t work properly.

Get enough sleep

Really - get enough sleep. Plan in your daily routine when you’re going to bed. Sometimes it is in fact not possible to sleep enough. As long as this is the exception, everything is fine. It should simply not be the rule. At the latest when you’re constantly falling asleep during lectures you should rethink your sleeping habits.

Do something that gives you compensation

You need to get your head free. Often you think about a physics problem for hours and stay struck, even after discussing with your mates. Get a hobby or better to say, don’t stop the hobbies you’ve been doing before. Sports, drawing,… anything - but do something which is not physics.

Remember that it is possible to pass the exams

Although it might be difficult to believe in the beginning, it is really possible to pass. As long as your work hard enough. The exercise sheets are most of the time much harder than the exams. Get additional exercises from books etc. and you can properly learn for them. (Honest edit: Sometimes the exams seem actually impossible to pass. e.g. my linear algebra exam that 80% failed, but even then: you’re at least not alone).

Don’t compare yourself with others

Simply don’t start thinking that all the others are better than you. There are always these genius guys who seem to have less problems with the sheets and lectures. But these are no ordinary people and not the average student. It’s okay to belong to the struggling “mainstream”.

Don’t give up

Already after a few weeks you are going to see that there are many more free seats in the auditorium, because many guys give up. You need tenacious adherence to the idea that you do not belong to them because of the following:

Most important: Don’t forget why you are doing this!

All my points make physics look like some masochistic burden, but it is not. You are doing all of this in order to understand the world a bit better and get to the borders of human knowledge. It takes a lot of time and costs a lot - but it is worth it. I never regretted doing physics even in my most frustrated moments. I earnestly believe it’s the best you can study - your mind gets more analytically, you think outside the box and you see the fundaments of nature - even it is only a glance.

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physicla

3 years ago

Me Trying To Make Sense Of My Physics Book. Finishing An Exam Past Midnight. Notes For Class. New Cards!!

me trying to make sense of my physics book. finishing an exam past midnight. notes for class. new cards!!

i am. SO SO SO EXHAUSTED!!!! fighting for my life. and truly just waiting for the mid-semester break so i can spend my days sleeping xd

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physicla

3 years ago

26/01/22

100 days of productivity: 25/100

forgot to post yesterday but here are my phys notes!!

📍place of the day: Golden Gates, San Francisco

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physicla

3 years ago

18.07.2021//

How to reuse old rational mechanics notes:

Pick your old notes

Enjoy destroying them

Drown them in the water and blend

Make your own frame with woods and a mosquito net 🦟

Use the frame to make perfect sheets

Wait 73839393 hours

When they are dried be careful and don’t rip them off

Write down your personal theory of everything

Win the Nobel

Use the remaining recycled paper to dry your happy tears

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physicla

3 years ago

Radio Astronomy

So I learnt something really cool today. Radio astronomy. Radio astronomy is done at ~ 1.4 GHz frequency. WHY YOU ASK??? Because hydrogen is the most abundant element in the universe!!! And hydrogen atoms have one electron !! Electrons possess spins!! Spins can flip!! And when they do, they emit a wavelength of 21 cm!! Which corresponds to a frequency of 1.4 GHz (f = c/λ). And since hydrogen is basically EVERYWHERE, they use that to observe celestial bodies and it is a very protected frequency which means radio stations, satellites and cellphone towers can't use it!!

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