Chandra determines what makes up the wind of NGC 253 is a spiral galaxy?

 

On Earth, wind can have a major impact on the environment, transporting particles of dust, sand, and debris across the planet. Now a new study has revealed an even more dramatic effect of wind on a galaxy – 11.4 million light-years away from Earth. Using NASA’s Chandra X-ray Observatory, researchers have detected powerful winds from the center of the galaxy NGC 253 that have temperatures of millions of degrees and are composed of glowing X-ray gas. This wind is capable of transporting two million Earth masses away from the galaxy’s center every year, making it one of the most powerful galactic winds ever observed. This study is helping understand how wind can drastically alter the ecology and environment of galaxies, just like it does here on Earth.

NGC 253 is a spiral galaxy, similar in many ways to our own Milky Way. However, star formation in this galactic structure is much more active, with stars forming two to three times faster than in the Milky Way. These young stars, which are generally more massive than the stars in our home galaxy, release a powerful wind of gas from their surfaces. Even more powerful winds are unleashed when these stars eventually explode as supernovae and send powerful shockwaves of material out into space. NGC 253 is a remarkable star-forming region in the southern sky, providing astronomers with a unique vantage point to observe the stars in their crucial formative stages. The young stars in this region are releasing material into space, enriched with elements that were created within them. These elements are essential for the formation of the next generations of stars and planets, and they even contribute to life on Earth.

This composite image of NGC 253 is an incredible view of our universe. In the inset, Chandra data is displayed in both pink and white, showing that winds in this galaxy blow in two opposite directions away from the center. Visible light data from a 0.9 meter telescope at Kitt Peak Observatory is shown in cyan and emission from hydrogen is shown in orange. Red colors come from infrared data from NASA’s Spitzer Space Telescope. The wider image shows an optical image of NGC 253 from the European Southern Observatory’s La Silla Observatory in Chile, giving us an edge-on glimpse of this remarkable galaxy. The combination of data gives us an amazing insight into the space around us and makes it possible to observe a galaxy as far away as NGC 253 with such clarity.

The bright center of the spiral galaxy NGC 253.

A team of researchers led by Sebastian Lopez from The Ohio State University in Columbus, Ohio, recently used deep Chandra observations taken over a four-day period to study the properties of a galactic wind. The results of the study revealed that the densities and temperatures of the gas in the wind were highest in regions closer to the center of the galaxy at distances of less than 800 light-years, before decreasing with distance further away. The results of recent work on the wind formation from starburst galaxies like NGC 253 have been found to be in stark disagreement with an early model that suggested they are spherical. Instead, it has been predicted that a more focused wind is formed by a concentric ring of “super star clusters” located near the center of NGC 253, This is due to super star clusters containing a high number of young, massive stars.

The focused nature of the wind observed by Lopez and his team supports the idea that the super star clusters are a major source of the wind. However, there is not complete agreement between theory and observations, meaning there is some physics missing from the theory. An observation from the team that the wind cools rapidly as it moves away from the center of the galaxy may point to what is missing. This cooling effect suggests that the wind is ‘plowing up’ cooler gas, thus cooling and slowing down. This ‘wind plow’ effect might be the additional physics required to achieve a better agreement between theory and observations. While more research is needed to confirm this hypothesis, the evidence is compelling that this phenomenon could explain why there is not a perfect match between theory and observations.

Lopez and his colleagues conducted an extensive study of the composition of the wind in one particular galaxy, finding that elements such as oxygen, neon, magnesium, silicon, sulfur and iron were all much less abundant farther away from the center. Surprising to the researchers, this decrease was not seen in another well-studied galaxy that is currently undergoing a burst of star formation, M82. In order to understand why this difference exists and if it is related to the total mass of stars contained within each galaxy, future observations of other galaxies with winds need to be conducted.

A team of renowned astrophysicists, including Sebastian Lopez, Laura Lopez, Dustin Nguyen, Todd Thompson, Smita Mathur (The Ohio State University), Alberto Bolatto (University of Maryland, College Park), Neven Vulic (Eureka Scientific) and Amy Sardone (Ohio State) have recently published their findings in The Astrophysical Journal. The paper is available online and provides an in-depth analysis of the Chandra program, managed by NASA’s Marshall Space Flight Center. The Chandra X-ray Center, established by the Smithsonian Astrophysical Observatory, is responsible for the flight and science operations from Cambridge, Massachusetts, and Burlington, Massachusetts respectively. This enlightening paper provides a comprehensive insight into the Chandra program, which is a major advancement in the field of astrophysics.