Normal Galaxies & Starburst Galaxies

NGC 4839
Credit: X-ray: Chandra: NASA/SAO/Univ. of Alabama/M. S. Mirakhor et al.; XMM: ESA/XMM-Newton;
Optical: SDSS; Image processing: N. Wolk

A group of galaxies is plunging into the Coma galaxy cluster and leaving behind an enormous tail of superheated gas. Astronomers have confirmed this is the longest known tail behind a galaxy group and used it to gain a deeper understanding of how galaxy clusters – some of the largest structures in the universe – grow to their enormous sizes.

NGC 253
Credit: X-ray: NASA/CXC/The Ohio State Univ/S. Lopez et al.; H-alpha and Optical: NSF/NOIRLab/AURA/KPNO/CTIO; Infrared: NASA/JPL-Caltech/Spitzer/D. Dale et al; Full Field Optical: ESO/La Silla Observatory.

On Earth, wind can transport particles of dust and debris across the planet, with sand from the Sahara ending up in the Caribbean or volcanic ash from Iceland being deposited in Greenland. Wind can also have a big impact on the ecology and environment of a galaxy, just like on Earth, but on much larger and more dramatic scales.

A new study using NASA's Chandra X-ray Observatory shows the effects of powerful winds launched from the center of a nearby galaxy, NGC 253, located 11.4 million light-years from Earth. This galactic wind is composed of gas with temperatures of millions of degrees that glows in X-rays. An amount of hot gas equivalent to about two million Earth masses blows away from the galaxy's center every year.

NGC 253 is a spiral galaxy, making it similar to our Milky Way. However, stars are forming in NGC 253 about two to three times more quickly than in our home galaxy. Some of these young stars are massive and generate a wind by ferociously blowing gas from their surfaces. Even more powerful winds are unleashed when, later in their relatively short lives, these stars explode as supernovae, and hurl waves of material out into space.

Valentina Missaglia

We are happy to welcome Valentina Missaglia as a guest blogger. She is the first author of the paper that is the subject of our latest press release. She is currently a postdoctoral researcher at the Institute of Astrophysics — FORTH in Heraklion (Crete) in the SMILE (“Search for Milli-LEnses”) group, recently funded by an ERC grant, that aims at investigating the nature of dark matter through observations of gravitational lenses on milli-arcsecond scales. Valentina earned her Ph.D. from the University of Turin (Italy) and her research focuses on radio and X-ray emission from radio-loud active galactic nuclei (which contain supermassive black holes that are rapidly pulling in material, producing intense radio waves) and how these sources interact with the surrounding medium. Before starting her Ph.D. in 2019, Valentina was a visiting student at the Center of Astrophysics | Harvard & Smithsonian, where she collaborated with Dr. Ralph Kraft on observations of galaxy clusters performed with NASA’s Chandra X-ray Observatory.

Looking at the night sky with the naked eye, we can only see an infinitesimal part of what the Universe contains, and the largest part cannot even be “seen”. Radio wavelengths have gifted us some of the most fascinating astronomical sources: radio-loud active galactic nuclei in the centers of galaxies, which can produce jets that extend way farther out from the optical galaxy itself.

The most powerful radio sources in the northern hemisphere are listed in a well- studied catalog, the Third Cambridge Catalog (3C), which contains the source we investigated with multiwavelength observations: 3C 297. This source appeared very intriguing in observations performed with Chandra in 2016. Therefore, we requested more time to better investigate features that we uncovered thanks to this first short observation, such as hot, X-ray emitting gas around our source.

SDSS J011522.18+001518.5 and SDSS J155627.74+241758.9
Credit: X-ray: NASA/CXC/SAO/D. Kim et al.; Optical/IR: Legacy Surveys/D. Lang (Perimeter Institute)

This panel of images represents a survey that used data from NASA’s Chandra X-ray Observatory to uncover hundreds of previously “hidden” black holes. This result helps astronomers conduct a more accurate census of supermassive black holes that exist in the centers of most large galaxies, as reported in our latest press release.

This graphic shows two of the galaxies from the new study, with Chandra X-ray data in purple and optical data from the Sloan Digital Sky Survey (SDSS) in red, green and blue. These black holes were found in galaxies that are dim in optical light, but bright in X-rays. Astronomers have dubbed these “XBONGs” (for X-ray bright, optically normal galaxies). While scientists have been aware of XBONGs for several decades, an explanation for their unusual properties has been unclear.

Vivienne Baldassare

We are happy to welcome Vivienne Baldassare as our guest blogger. Vivienne is an Assistant Professor of Physics and Astronomy at Washington State University, and led the paper that is the subject of our latest press release. Her work is mainly focused on searching for the smallest supermassive black holes in order to learn more about black hole formation and growth. Prior to her current position, she was a NASA Einstein fellow at Yale University. She earned her PhD in Astronomy & Astrophysics from the University of Michigan in 2017, and a bachelor's degree in Physics from CUNY Hunter College in 2012.

One of the biggest open questions in astrophysics is “how do massive black holes form?” Our recent research with NASA’s Chandra X-ray Observatory provides support for the theory that massive black holes can form in what astronomers call nuclear star clusters.

While big galaxies have supermassive black holes at their centers, small galaxies often have a nuclear star cluster. Nuclear star clusters are extremely dense, with millions of stars packed into a region that is tens of light years across. It was once suggested that supermassive black holes and nuclear star clusters may be mutually exclusive, with the former residing in big galaxies and the latter occurring in small galaxies. However, some galaxies (like our Milky Way!) have been found to contain both. And excitingly, some theories suggest that nuclear star clusters might be able to form massive black holes.

In my first year of graduate school, I carried out a project studying the properties of nuclear star clusters. After that, I transitioned to studying massive black holes in dwarf galaxies, but have always had a soft spot for these fascinating objects. Our new study brought these two areas together.