Astronomers discovered a black hole unlike any other. At one hundred thousand solar masses, it is smaller than the black holes we have found at the centers of galaxies but bigger than the black holes that are born when stars explode. This makes it one of the only confirmed intermediate-mass black holes, an object that has long been sought by astronomers.

Anil Seth

“We have very good detections of the biggest, stellar-mass black holes up to 100 times the size of our sun, and supermassive black holes at the centers of galaxies that are millions of times the size of our sun, but there aren’t any measurements of black between these. That’s a large gap,” said senior author Anil Seth, associate professor of astronomy at the University of Utah and co-author of the study. “This discovery fills the gap.”

The black hole was hidden within B023-G078, an enormous star cluster in our closest neighboring galaxy Andromeda. Long thought to be a globular star cluster, the researchers argue that B023-G078 is instead a stripped nucleus. Stripped nuclei are remnants of small galaxies that fell into bigger ones and had their outer stars stripped away by gravitational forces. What’s left behind is a tiny, dense nucleus orbiting the bigger galaxy and at the center of that nucleus, a black hole.

“Previously, we’ve found big black holes within massive, stripped nuclei that are much bigger than B023-G078. We knew that there must be smaller black holes in lower mass stripped nuclei, but there’s never been direct evidence,” said lead author Renuka Pechetti of Liverpool John Moores University, who started the research while at the U. “I think this is a pretty clear case that we have finally found one of these objects.”

The study published on Jan. 11, 2022, in The Astrophysical Journal.

A decades-long hunch

B023-G078 was known as a massive globular star cluster—a spherical collection of stars bound tightly by gravity. However, there had only been a single observation of the object that determined its overall mass, about 6.2 million solar masses. For years, Seth had a feeling it was something else.

“I knew that the B023-G078 object was one of the most massive objects in Andromeda and thought it could be a candidate for a stripped nucleus. But we needed data to prove it. We’d been applying to various telescopes to get more observations for many, many years and my proposals always failed,” said Seth. “When we discovered a supermassive black hole within a stripped nucleus in 2014, the Gemini Observatory gave us the chance to explore the idea.”

A wide-field image of M31 with the red box and inset showing the location and image of B023-G78 where the black hole was found.

With their new observational data from the Gemini Observatory and images from the Hubble Space Telescope, Pechetti, Seth and their team calculated how mass was distributed within the object by modeling its light profile. A globular cluster has a signature light profile that has the same shape near the center as it does in the outer regions. B023-G078 is different. The light at the center is round and then gets flatter moving outwards. The chemical makeup of the stars changes too, with more heavy elements in the stars at the center than those near the object’s edge.

“Globular star clusters basically form at the same time. In contrast, these stripped nuclei can have repeated formation episodes, where gas falls into the center of the galaxy, and forms stars. And other star clusters can get dragged into the center by the gravitational forces of the galaxy,” said Seth. “It’s kind of the dumping ground for a bunch of different stuff. So, stars in stripped nuclei will be more complicated than in globular clusters. And that’s what we saw in B023-G078.”

The researchers used the object’s mass distribution to predict how fast the stars should be moving at any given location within the cluster and compared it to their data. The highest velocity stars were orbiting around the center. When they built a model without including a black hole, the stars at the center were too slow compared their observations. When they added the black hole, they got speeds that matched the data. The black hole adds to the evidence that this object is a stripped nucleus.

“The stellar velocities we are getting gives us direct evidence that there’s some kind of dark mass right at the center,” said Pechetti. “It’s very hard for globular clusters to form big black holes. But if it’s in a stripped nucleus, then there must already be a black hole present, left as a remnant from the smaller galaxy that fell into the bigger one.”

The researchers are hoping to observe more stripped nuclei that may hold more intermediate-mass black holes. These are an opportunity to learn more about the black hole population at the centers of low-mass galaxies, and to learn about how galaxies are built up from smaller building blocks.

“We know big galaxies form generally from the merging of smaller galaxies, but these stripped nuclei allow us to decipher the details of those past interactions,” said Seth.

Other authors include Sebastian Kamann of the Liverpool John Moores University; Nelson Caldwell, Harvard-Smithsonian Center for Astrophysics; Jay Strader, Michigan State University; Mark den Brok, Leibniz-Institut für Astrophysik Potsdam; Nora Luetzgendorf, European Space Agency; Nadine Neumayer, Max Planck Institüt für Astronomie; and Karina Voggel, Observatoire astronomique de Strasbourg.

- by Lisa Potter, published in @theU and the Deseret News

In December 2020 the James Webb Space Telescope (JWST) finally launched. The $10 billion observatory is a twenty-year joint effort of NASA, the European Space Agency, and the Canadian Space Agency, and the most powerful telescope ever developed. Its mission—peer 13.5 billion lightyears back in time to the earliest stages of the universe.

Anil Seth

JWST’s launch date was December 25 from Europe’s Spaceport in Kourou, French Guiana. Longtime fans of the telescope are celebrating it as a Christmas miracle. It was the first planned to launch in 2007, but decades of delays and false hope drove the project from its initial budget of $500 million up to its current $10 billion cost.

You can watch recorded launch video and future NASA livestreams at  https://www.nasa.gov/nasalive.

The stakes are high for Anil Seth, associate professor in the Department of Physics & Astronomy. Out of more than 1,000 proposals for observation time on the telescope, Seth’s is one of 266 that were approved. He spoke with AtTheU to talk about this cosmic milestone.

What is the James Webb Space Telescope?

It is the largest and most powerful telescope that we’ve ever sent into space—the primary mirror is about the size of a typical house. It’s really big compared to the Hubble Space Telescope, which has a primary mirror the size of a bedroom. Hubble uses the ultraviolet and visible light to create jaw-dropping images of deep space that fundamentally changed our understanding of the cosmos. JWST will be much, much, much farther away than Hubble, located almost one million miles from Earth. From there, it can detect the faintest traces of infrared light, the wavelength of light emitted by everything that produces heat.

NASA assembly, July 2017

The telescope’s primary power is to detect faint galaxies far, far away. It’ll be able to pick up the infrared light spectrum of planets, newly forming stars, black holes, and other faint objects in ways that we’ve never been able to before. Almost every astronomer is probably going to want to use JWST for something. We saw so much using the Hubble Space Telescope. With JWST, we’ll be able to see more than we can imagine. It’s very exciting.

The launch date has been pushed back several times including once this week. Is the telescope launch tricker then usual?

The size makes it really hard to launch. The telescope has three big segments—a sunshield the size of a tennis court, the house-sized primary mirror, and the secondary mirror, Right now, it’s all packaged up like a Christmas present to fit inside the rocket. After launch, the segments will begin to unfold. It’s a complicated process involving hundreds of steps that have to work perfectly. This has never been done before—one error and the whole project could fail. That’s why people are so stressed out!

Where will JWST orbit in space?

It’s going to orbit the sun almost one million miles away from Earth. It will live at what is called a Lagrange point, a location where gravity from the earth and sun are equal. And will just sit there, orbiting with the Earth around the sun. This ensures that the telescope will always point away from the sun.

Full-scale model, September 2005

Anything warm emits infrared light—stars, humans, every other thing on Earth. To make an infrared-detecting telescope, the equipment needs to be extremely cold, so its heat doesn’t interfere with infrared readings from space. That’s what the sun shield is for. The massive mylar sail will create a shadow that prevents the telescope from absorbing heat. The sunshade will begin to unfurl a week after launch, starting with 107 release mechanisms that have to fire simultaneously. The sun shield will then always be between the telescope and sun, keeping the telescope really cold. If this doesn’t happen right…it’ll be bad.

JWST’s location also provides a wide-open view for observations. The Hubble space telescope orbits the Earth just over 300 miles up, which means the planet sometimes blocks the telescope’s vision as it orbits the earth every 90 minutes. At JWST’s Lagrange position, it’s much easier to keep a single orientation in the sky for a longer time and to make observations constantly. So we’ll end up getting more data each year from JWST than from Hubble.

You will be one of the first astronomers to get observation time on the JWST. Can you tell us about your research?

I study black holes. Every black hole has stuff falling onto it that emits light. It turns out that a lot of that light gets emitted at infrared wavelengths. This telescope is much, much, more sensitive to those wavelengths than any other previous telescope. The problem is that we’ve never seen what a faint black hole looks like at these wavelengths.

The Andromeda Galaxy, approximately 2.5 million light-years from Earth.

I’m leading a project that will look at places where we know black holes exist, because we’ve measured them from the motions of the stars around them, but that are very faint. These are so much fainter than something like a quasar, which is where the black hole is devouring as much material as it can. The black holes I’m interested in are just sipping their material, and they’re much more typical of the average black hole in the universe. We’re basically looking unique signatures in this wavelength spectrum that will tip us off to a black hole is present. One of the objects we’ll focus on is the first one ever photographed.

- by Lisa Potter, first published at @theU

NASA J.W.S.T. VIDEO