NASA's Chandra X-ray Observatory detects X-ray emissions from astronomical events. Credit: NASA/CXC and J. Vaughan.
When a star is born or dies, or when any other highly energetic phenomenon occurs in the universe, emits x rays, which are high-energy light particles that are not visible to the naked eye. These x-rays are of the same type. What do doctors use? to take photographs of broken bones inside the body. But instead of looking at the shadows produced by bones that stop X-rays inside a person, astronomers detect X-rays flying through space to image events like black holes and supernovae.
Images and spectra (graphs that show the distribution of light at different wavelengths from an object) are the two main ways astronomers investigate the universe. The images tell them how things look and where certain phenomena are happening, while the ghosts tell them how much energy the photons, or light particles, have that they are collecting. Spectra can tell you how the event they came from was formed. When studying complex objects, they need both images and spectrums.
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.
Stars forming and dying create supernova explosions that send chemical elements into space. Chandra observes how gas and stars falls into the deep gravitational forces of black holes, and bears witness to this when gas a thousand times hotter than the Sun escapes from galaxies in explosive winds. It can be seen when the gravity of huge masses of dark matter traps that hot gas in gigantic pockets.
NASA designed Chandra to orbit the Earth because it wouldn't be able to see any of this activity from the Earth's surface. Earth's atmosphere absorbs X-rays coming from space, which is great for life on Earth because these X-rays can damage biological organisms. But it also means that even if NASA placed Chandra on top of the tallest mountain, it still wouldn't be able to detect X-rays. NASA needed 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 its launch 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 holeswhich have masses of ten to 100 million times that of our Sun, in the centers of all galaxies. These supermassive black holes are mostly there peacefully, and astronomers can detect them by observing the gravitational pull they exert on nearby stars.
But sometimes stars or clouds fall into these black holes, which activates them and causes the region near the black hole to emit many 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 its black hole becomes an AGN. We choose a galaxy ESO 428-G014to watch with Chandra.
An AGN can eclipse its host galaxy, meaning that more light comes from the AGN than from all the stars and other objects in the host galaxy. AGN also deposits a lot of energy within the boundaries of its host galaxy. This effect, what astronomers call feedback, is an important ingredient for researchers who are creating simulations that model how the universe evolves over time. But we still don't know what role an AGN's energy plays in star formation in its host galaxy.
Fortunately, Chandra images can provide important information. I use computational techniques to construct and process images from the observatory that can inform me about these AGN.
The active supermassive black hole in ESO 428-G014 produces X-rays that illuminate a large area, extending up to 15,000 light years away from the black hole. The basic image I generated. from ESO 428-G014 with Chandra data It tells me that the region near the center is the brightest and that there is a large, elongated region of X-ray emission.
The same data, at slightly higher resolution, show two distinct regions with high X-ray emissions. There is a “head,” encompassing the center, and a slightly curved “tail” extending downward from this central region.
I can also process the data with an adaptive smoothing algorithm that brings the image to even higher resolution and creates a clearer image of what the galaxy looks like. This shows clouds of gas around the bright center.
My team has been able to see some of the ways the AGN interacts with the galaxy. The images show nuclear winds sweeping the galaxy, dense clouds and interstellar gas reflecting X-ray light, and jets firing radio waves that heat the galaxy's clouds.
These images teach us how this feedback process works in detail and how to measure how much energy an AGN deposits. These results will help researchers produce 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 rely on Chandra to answer questions about the origin of the universe that no other telescope can answer.
By providing astronomers with X-ray data, Chandra data complements information from the Hubble space telescope and the James Webb Space Telescope give astronomers unique answers to open questions in astrophysics, such as where the supermassive black holes found at the centers of all galaxies come from.
For this particular question, astronomers used Chandra to observe a distant galaxy first observed by the James Webb Space Telescope. This galaxy emitted the light captured by Webb 13.4 billion years ago, when the universe was young. Chandra X-ray data revealed a bright supermassive black hole in this galaxy and suggested that supermassive black holes may form by the Collapsed clouds in the early universe..
Sharp images have been crucial to these discoveries. But Chandra is expected to will only last another 10 years. To keep up the search for answers, 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 firm plans to do so.
This article was first published in The conversation. It is republished here under a Creative Commons license.
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