When a star is born or dies, or any other highly energetic phenomenon occurs in the universe, it emits X-rays, which are high-energy particles of light that are not visible to the naked eye. These X-rays are the same kind that doctors use to take pictures of broken bones in the body. But instead of looking at the shadows produced by the bones that block X-rays in a person, astronomers detect X-rays flying through space to get images of events such as black holes and supernovae.
Images and spectra – graphs that show an object’s distribution of light across different wavelengths – are the two main ways astronomers explore the universe. Images tell them what things look like and where certain phenomena occur, while spectra tell them how much energy the photons, or light particles, they collect have. Spectra can give them insight into how the event they came from came to be. When studying complex objects, they need both imaging and spectra.
Scientists and engineers designed the Chandra X-ray Observatory to detect these X-rays. Since 1999, Chandra data has provided astronomers with incredibly detailed images of some of the most dramatic events in the universe.
The formation and death of stars causes supernova explosions that send chemical elements into space. Chandra watches as gas and stars fall into the deep gravity of black holes, testifying that gas a thousand times hotter than the Sun escapes from galaxies in explosive winds. It can tell when the gravity of huge masses of dark matter traps that hot gas in giant pockets.
NASA designed Chandra to orbit Earth because it would not be able to see this activity from Earth’s surface. Earth’s atmosphere absorbs X-rays coming from space, which is great for life on Earth because these X-rays can harm biological organisms. But it also means that even if NASA placed Chandra on the highest mountain peak, it still wouldn’t be able to detect X-rays. NASA had to send Chandra into space.
I am an astrophysicist at the Smithsonian Astrophysical Observatory, part of the Center for Astrophysics | Harvard and Smithsonian. I’ve been working on Chandra since before it was launched 25 years ago, and it’s been a pleasure to see what the observatory can teach astronomers about the universe.
Supermassive black holes and their host galaxies
Astronomers have found supermassive black holes in the centers of all galaxies, which have a mass ten to a hundred million times that of our Sun. These supermassive black holes usually reside there peacefully, and astronomers can detect them by looking at the gravity they exert on nearby stars.
But sometimes stars or clouds fall into these black holes, activating them and causing the area close to the black hole to emit a lot of X-rays. Once activated, they are called active galactic nuclei, AGN or quasars.
My colleagues and I wanted to better understand what happens to the host galaxy once the black hole turns into an AGN. We picked one galaxy, ESO 428-G014, to look at with Chandra.
An AGN can outshine its host galaxy, meaning it emits more light from the AGN than all the stars and other objects in the host galaxy. The AGN also deposits a lot of energy within the boundaries of its host galaxy. This effect, which astronomers call feedback, is a key ingredient for researchers building simulations that model how the universe evolves over time. But we still don’t know exactly what role an AGN’s energy plays in the formation of stars in its host galaxy.
Fortunately, images of Chandra can provide important insight. I use computer techniques to build and process images from the observatory that can tell me about these AGNs.
The active supermassive black hole in ESO 428-G014 produces X-rays that illuminate a large area up to 15,000 light-years away from the black hole. The basic image I generated of ESO 428-G014 with Chandra data tells me that the region near the center is the brightest and that there is a large, elongated region where X-rays are emitted.
The same data, at slightly higher resolution, shows two different areas of high X-ray emission. There is a ‘head’ that encompasses the center, and a slightly curved ‘tail’ that extends downward from this central area.
I can also process the data with an adaptive smoothing algorithm that brings the image into even higher resolution and creates a clearer picture of what the galaxy looks like. This shows gas clouds around the bright center.
My team was able to see some of the ways the AGN interacts with the Milky Way. The images show nuclear winds racing through the Milky Way, dense clouds and interstellar gas reflecting X-ray light, and jets shooting out radio waves that warm the clouds in the Milky Way.
These images teach us in detail how this feedback process works and how we can measure how much energy an AGN releases. These results will help researchers create more realistic simulations of how the universe evolves.
The next 25 years of X-ray astronomy
The year 2024 marks the 25th year since Chandra began making observations of the sky. My colleagues and I continue to depend on Chandra to answer questions about the origins of the universe that no other telescope can answer.
By providing astronomers with X-ray data, Chandra’s data complements information from the Hubble Space Telescope and the James Webb Space Telescope to give astronomers unique answers to open questions in astrophysics, such as where the supermassive black holes at the centers of all galaxies came from. by.
For this specific question, astronomers used Chandra to observe a distant galaxy first spotted by the James Webb Space Telescope. This galaxy emitted the light that Webb captured 13.4 billion years ago, when the universe was still young. Chandra’s X-ray data revealed a bright supermassive black hole in this galaxy and suggested that supermassive black holes could be formed by the collapsing clouds in the early Universe.
Sharp imaging has been crucial to these discoveries. But Chandra is expected to last only another ten years. To keep the search for answers going, astronomers will have to start designing a “super Chandra” X-ray observatory that could succeed Chandra in the coming decades, although NASA has not yet announced any concrete plans to do so.
This article is republished from The Conversation, an independent nonprofit organization providing facts and trusted analysis to help you understand our complex world. It was written by: Giuseppina Fabbiano, Smithsonian attitude
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Giuseppina Fabbiano receives funding from NASA, SI, NSF.