Normal Galaxies & Starburst Galaxies

Mustafa Muhibullah (Credit: Mustafa Muhibullah)

We welcome Mustafa Muhibullah as a guest blogger. He is the first author of a Nature Astronomy paper that is the subject of our latest press release. Mustafa is a Ph.D. candidate in Physics & Astronomy at the University of Alabama, working with Prof. Jimmy Irwin since Fall 2021. His research focuses on high-energy astrophysics, particularly faint and compact X-ray sources and galaxy clusters, using NASA’s Chandra X-ray Observatory. He earned his M.S. in Physics from the University of Missouri–Kansas City in 2021 and his B.S. in Mechanical Engineering from Rajshahi University of Engineering & Technology, Bangladesh.

The “Unobserved” Window of the Universe

Modern astronomy explores the Universe across nearly the entire electromagnetic spectrum, from radio waves to X-rays. Yet one important window remains largely hidden: the extreme-ultraviolet (EUV), a narrow but energetic region between ultraviolet light and low-energy X-rays. For observers in the Milky Way, EUV radiation from distant sources is almost completely blocked by the cool, neutral hydrogen and helium that fill our Galaxy and readily absorbs these photons before they can reach our telescopes.

We know that powerful EUV emitters exist. For example, astronomers know that hot, massive stars, the solar corona, and active galaxies can all produce substantial EUV emission. Fortunately, they also radiate at other wavelengths, allowing astronomers to detect and study them even when their EUV light is absorbed.

The cosmos is full of surprises. When new classes of objects are discovered they can turn out to have more than one explanation. Some supernova explosions, for example, are triggered by the dramatic collapse of massive stars, while others involve the thermonuclear explosions of white dwarf stars. These two types of stars are remarkably different in size, mass, composition and density, but both can produce explosions that outshine entire galaxies. Another example is gamma ray bursts, which involve either the collapse of massive stars or the merger of two neutron stars.

The origin of the newly-discovered class of hypersoft X-ray sources is unknown, but similar diversity may apply. One leading idea is that many of them involve matter falling onto the surfaces of white dwarfs. Once the white dwarfs reach a sufficient mass they may explode as Type Ia supernovas, addressing the mystery of what triggers these spectacular explosions. In other words, some of these hypersoft X-ray sources may represent the build up to Type Ias — a very important category of supernovas that lets astronomers measure the accelerating expansion of the Universe. However, this explanation struggles to explain the brightest of the hypersoft X-ray sources.

Galaxy Gallery
More images and information
Credit: NASA/CXC/SAO

Galaxies are like cosmic gems, each with characteristics including size and shape that make them distinct. A new gallery released today from NASA’s Chandra X-ray Observatory and other telescopes displays a collection of galactic images that showcase this variety.

Astronomers put galaxies into three main categories: spirals like our own Milky Way with arms emanating from their cores, ellipticals that are older and likely the results of mergers, and irregulars that can encompass a wide range of galactic phenomena.

Just as gems reveal the history of Earth through how they were forged over billions of years, these galactic gems are a way to study Earth’s place in our home galaxy of the Milky Way. By looking outward to other galaxies, we learn more about our own – including clues to its past and future.

 
M83
More images, videos, and information
Credit: X-ray: NASA/CXC/SAO; Optical: NASA/ESA/AURA/STScI, Hubble Heritage Team, W. Blair (STScI/Johns Hopkins University) and R. O'Connell (University of Virginia); Image Processing: NASA/CXC/SAO/A. Jubett, L. Frattare and P. Edmonds

This graphic shows two of the X-ray sources in a nearby galaxy that are changing their brightness in surprising ways as described in our latest press release. By analyzing data from NASA’s Chandra X-ray Observatory that span over 14 years, researchers found over 20 previously identified supernova remnants — remains from stars that exploded — that vary unexpectedly in X-ray brightness in Messier 83 (M83). These represent roughly half of the X-ray sources associated with supernova remnants in their sample in M83.

The panel on the left contains a composite image of M83 with X-rays from Chandra (red, green, and blue) and optical light data from NASA’s Hubble Space Telescope (red, green, and blue). The two varying Chandra sources are circled in the composite image and close-up timelapse images of these sources are shown in the panels on the right.

Fall Image Collection
More images, videos, and information
Credit: NASA/CXC/SAO

Before fall gives way to winter in the northern hemisphere, NASA’s Chandra X-ray Observatory has several images that celebrate autumn and its many delights to share. In spirit of the season, this collection gathers Chandra data with those from its telescopic family including NASA’s James Webb, Hubble, and Spitzer Space Telescopes, plus others in space and on the ground.

Messier 106 (M106), also known as NGC 4258, is a spiral galaxy – like our own Milky Way -- located in the constellation Canes Venatici. It lies at a distance of roughly 23 million light-years and spans some 135,000 light-years in diameter.

This galaxy is famous, however, for something that our Galaxy doesn’t have – two extra spiral arms that glow in X-ray, optical, and radio light. These features, called anomalous arms, are not aligned with the plane of the galaxy, but instead intersect with it. The X-ray image from Chandra reveals huge bubbles of hot gas above and below the plane of the galaxy. These bubbles indicate that much of the gas that was originally in the disk of the galaxy has been heated to millions of degrees and ejected into the outer regions by the jets from a supermassive black hole at the galaxy’s core.

Credit: Optical: Deep Sky Collective; Chandra X-ray (purple): NASA/CXC/SAO;
VLA Radio (yellow): NSF/NRAO/VLA; Spitzer IR (Red): NASA/JPL-Caltech

It's not only space-based X-ray telescopes like Chandra, however, that have looked at M106. Excellent work has been done from the ground including by amateur astrophotographers including a group called the Deep Sky Collective (DSC). The DSC, founded by Tim Schaeffer in 2023, aims to use the group’s telescopes in a concerted way to explore some of the faintest and most difficult target in the sky in great detail.