Radio Astronomy

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.”

I made these for my Instagram page last year, and I'm just reposting these notes here. They are on the integral form of Gauss' law, the first of Maxwell's equations. I guess this would have been better explained in a video but oh well.

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)

self portrait

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

Thankyou :-)

'No-one gets ink stains like yours out of a desire for money.'

Jo March, a protagonist of Louisa May Alcott's novel 'Little Women'

Ambition can dig like a needle; mostly, you have to pull a dream forward, but sometimes it pushes you. And it prods and bites and stings when things seem hopeless; when you have aspirations, the thought of them wilting wounds you like nothing else.

Life can seem like a series of wounds.

Much like ambition, the longing for love both pulls and pushes— but in which direction, who can say? The bright winds of freedom seem harsh without a hand to hold; and yet, the brightness of Summer love smothers without them.

for @hallucinating-antonym

send me a ☀️ if you want a poem about a protagonist or antagonist that your blog reminds me of

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

31/01/22

100 days of productivity: 31/100

happy lunar new year!!! 🧧🧧🧧

Art by Simone Ferriero

reviewing physics notes bc an exam is in a few days. whenever i don't want to work, i take a deep breath and just tell myself this will be worth it in the end.. 👍