BAN #317: Uneven black holes merge, Adolescent eagle

26 April 2021   Issue #317

[The planetary nebula M 2-9, winds from a dying star. Credit: NASA / ESA / Hubble Legacy Archive / Judy Schmidt]

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Astro Tidbit

A brief synopsis of some interesting astronomy/science news

In 2019, the LIGO/Virgo gravitational wave observatories detected a faint ripple in the fabric of spacetime passing over the Earth. This event was dubbed GW 190521 (a gravitational wave detected on May 21, 2019) and analyzing the signal, astronomers determined it was caused by the merger of two black holes, one 66 times the mass of the Sun and the other 85 times its mass.

That’s a problem, because getting a black hole 85 times the mass of the Sun is difficult. Black holes like this form when a massive star explodes, and the star core collapses to form the black hole. This works for cores up to about 65 times the Sun’s mass, but when they get more massive than that weird physics comes into play. Basically, for cores 65 – 135 times the Sun’s mass, the core explodes along with the star leaving no black hole behind.

So that 85 solar-mass black hole is a problem. Maybe it formed from the previous merger of two lower mass black holes. Possible, but that’s a pretty rare event too. If you want details I wrote about this on the blog when it was announced.

A new paper has been published that might resolve the issue. The idea has to do with how the black hole masses are measured in a merger. The gravitational wave signal has a certain shape to it, like a sine wave. The amplitude (wave height), wavelength (distance between wave crests), and overall shape all depend on the two black holes merging, their distance form us, and how they spiral into one another. Using computer models, scientists basically created a massive database of simulated gravitational wave signals, where each is from a specific type of merger. Then, when a real one is detected, it can be compared to the database statistically to find the best fit.

In the new paper the astronomers show that there are two good fits to the detected wave. One is the one that was initially published, with a 66/85 solar mass black hole pair.

[Statistical model fits to the detected black hole merger on May 21, 2019 include a 66/85 solar mass merger (in blue) and a 170/16 solar mass one (orange). Both fit the data pretty well. The three signals are from the two LIGO facilities (in Livingston, Louisiana and Hanford, Washington) and the Virgo observatory in Europe. Credit: Nitz and Capano]

But the other model that fits well is an odd couple: a 16 solar mass black hole merging with a whopping 170 solar mass one! Although that’s truly a massive beast, it’s well outside the range where black holes don’t form in supernova explosions. It would take a monster star to create a black hole like that, but at least it’s possible.

Black holes more massive than 100 Suns are what we call intermediate mass black holes (or IMBH) between ones created by a star exploding (stellar mass black holes) and supermassive ones in galaxy centers, which are 100,000 Suns or more. IMBHs are difficult to detect and although there are many candidates, no conclusive detection has been made of one.

If this is the case then this would be the first detection of what’s called an intermediate mass-ratio inspiral, where a much bigger black hole arte a smaller one. Most mergers we see are from black holes of roughly the same mass, or maybe a mass ratio of 2. This one looks to be at least 5, so the two components are far different masses.

Interestingly, weeks after the merger, a flare of energy was seen from the same part of the sky. It was traced to a galaxy about 4.6 billion light years away. If this indeed came from the merger somehow, that’s an independent measure of the distance! When they include that in their analysis they find the statistics favor the 170/16 solar mass merger even more. But it’s not clear if the flare is associated with the merger or not.

Either way, this is cool. It either started with an IMBH to get a slightly bigger one, or it started with an unlikely mass for a black hole, and whichever is correct it means this was a pretty interesting event. At the very least it seems to show that we need to be careful when assigning masses to the black holes in a merger. There could be hidden cool events out there masquerading as another kind of cool event.

Blog Jam

What I’ve recently written on the blog, ICYMI

[The distorted view of two black holes orbiting each other, the light warped by the intense gravity of both. From Tuesday’s article. Credit: NASA’s Goddard Space Flight Center/Jeremy Schnittman and Brian P. Powell]

Monday 19 April, 2021: Mars Ingenuity takes flight! Watch the first out-of-this-world video

Tuesday 20 April, 2021: Watch the doubly warped view of two monster black holes orbiting each other

Wednesday 21 April, 2021: Astronomers find an exoplanet where an exoplanet shouldn’t be

Thursday 22 April, 2021: In a technological first, NASA has made a sip of breathable air on Mars

Friday 23 April, 2021: Millions of black holes are in our galaxy. Here’s how we’ll find some of them.

Red in Tooth and Claw

I live in rural Colorado, and we get nature here

There is a series of poles running down the road to my house, and sometimes birds like to sit on them to get an overview of the area (they probably think of it as the pantry). There’s one in particular that eagles love to sit on, which we call (duh) the eagle pole… so I was surprised recently to see a gigantic bird sitting on a different pole, one closer to us. I had never seen one sitting there, so I grabbed the camera:

[A bald eagle sitting on a power pole. Credit: Phil Plait]

Despite this pole being closer to me this was a tough shot. It was overcast, drizzly, and pretty gloomy, and, as usual, I didn’t have time to get the camera on a tripod so the photo is a little grainy and the contrast low. Still, cool.

This is actually a bad eagle! It’s young, probably 3 years or so. At that age they’re still on their way to getting the full white head and tail, and the yellow beak. This one is halfway there, with white and brown mottled head feathers. The half-yellow/half-black beak is so odd looking! But by next summer this bird will be fully adult, or pretty close.

It already has the imperious lord-of-all-I-survey glare down pat, though.

Et alia

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