Searching the sky for black holes with the world’s most powerful space telescope


Allison Kirkpatrick had just two days to survey parts of the cosmos using the James Webb Space Telescope (JWST), the most powerful space telescope ever created, and its mid-infrared instrument to search for supermassive black holes.

Kirkpatrick, an associate professor of physics and astronomy, was the first to explore an area of space called “the Extended Groth Strip” for these supermassive black holes, where she used the James Webb Space Telescope to search for them at the center of galaxies. 

Studies like these are critical to expand knowledge of black holes, offering insights into the development of galaxies and even the formation of the universe.

“I went looking for these galaxies and their average black holes and to see if these supermassive black holes grow in the same way they do in the most massive galaxies,” Kirkpatrick said. 

Kirkpatrick assumed that she would find many of these black holes and was surprised when she could not locate any. However, this steered her research in a new direction —  exploring if these black holes are growing at an extremely slow rate or if new techniques need to be developed to discover them. 

“The JWST has got incredible sensitivity and incredible resolution, so we can resolve really small details,” Kirkpatrick said. “For the first time we’re really able to take a galaxy like our Milky Way and put it back 10 billion years in the past and look at what’s happening inside of it.”

Telescopes in space, such as the JWST, can detect infrared light, which is part of the electromagnetic spectrum and is invisible to the human eye. The JWST is useful in detecting objects that cannot otherwise be seen with everyday telescopes. 

To detect a supermassive black hole with the JWST, scientists look for the material being pulled in by the black hole since it becomes extremely heated, Kirkpatrick said. The heated materials glow brightly due to the heat, allowing the JWST to identify the existence of it. 

With the 50 hours that she was awarded by a committee of astronomers to use the JWST, it opened its shutters and pointed to the region of the sky Kirkpatrick was studying. 

“Once we got the image, it took four or five months to get the final products that we used for science,” Kirkpatrick said. “We had to wait a while until more images had been built up to properly calibrate them.”

Greg Troiani, a graduate student working with Kirkpatrick, created figures to visualize the data produced by both the JWST and the Spitzer Space Telescope, another telescope designed to detect infrared radiation using SAOImage DS9, a program used to visualize astronomical data.

“One of the features it has is to produce RGB images — basically taking 3 different images, assigning a red/green/blue color to them, and overlaying them,” Troiani said. “The process here was to track down the images from Spitzer and JWST, apply this process and then tweak them until they looked nice.”

“You can see that these circles are tiny on JWST, compared to Spitzer — which tells us that JWST can make out much smaller and dimmer galaxies,” Troiani said. “The result itself isn’t that surprising; making a better IR telescope was the whole reason they built James Webb!”

Because the JWST is a new telescope, the raw data obtained by Kirkpatrick had to be processed to account for telescope noise to produce the final images. Telescope noise includes any specks or splotches in areas that should be smoothly toned.  

Kirkpatrick’s and Troiani’s research concluded that supermassive black holes are not growing very rapidly. Supermassive black holes may have been initially large and then gone through slow growth over time, or they may never have gone through a rapid growth phase. Kirkpatrick is set for another JWST project that will take place in March of next year, this time with 70 hours, leading to over 4,000 galaxies being observed. 

“I’ll look at the same region of the sky but looking at more of it,” Kirkpatrick said. “It’s hard to put together the truth when you only have a couple hundred galaxies.”


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