The dark heart of a cosmic collision

New observations strengthen the view that Centaurus A may have been created by the cataclysmic collision of two older galaxies.
By | Published: April 5, 2012 | Last updated on May 18, 2023
The peculiar galaxy Centaurus A in the far-infrared and X-rays. Inner structural features seen in this image are helping scientists to understand the mechanisms and interactions within the galaxy, as are the jets seen extending over thousands of light years from the black hole believed to be at its heart. Newly-discovered clouds co-aligned with the jets can also be seen in the far-infrared data, which are colored red and orange. The X-ray image data in this combined picture are shown in blue/cyan/purple and highlight the highly energetic jet region as well as structures that co-align with the far-infrared and X-ray jet (top left). Credit: Far-infrared: ESA/Herschel/PACS/SPIRE/C.D. Wilson, MacMaster University, Canada; X-ray: ESA/XMM-Newton/EPIC

Two of the European Space Agency’s (ESA) space observatories have combined to create a multiwavelength view of violent events taking place within the giant galaxy Centaurus A. The new observations strengthen the view that it may have been created by the cataclysmic collision of two older galaxies.

Centaurus A is the closest giant elliptical galaxy to Earth, at a distance of around 12 million light-years. It stands out for harboring a massive black hole at its core and emitting intense blasts of radio waves.

While previous images taken in visible light have hinted at a complex inner structure in Centaurus A, combining the output of two of ESA’s observatories working at almost opposite ends of the electromagnetic spectrum reveals the unusual structure in much greater detail.

Sir John Herschel observed the galaxy in 1847 during his survey of the southern skies. Now, more than 160 years later, the observatory bearing his family name has played a unique role in uncovering some of its secrets.

New images taken with the Herschel space observatory with unprecedented resolution at far-infrared wavelengths show that the giant black scar of obscuring dust crossing the center of Centaurus A all but disappears.

The images show the flattened inner disk of a spiral galaxy the shape of which scientists believe is due to a collision with an elliptical galaxy during some distant, past epoch.

The Herschel data also uncover evidence for intense star birth toward the center of the galaxy along with two jets emanating from the galaxy’s core — one of them 15,000 light-years long. Newly discovered clouds co-aligned with the jets can also be seen in the far-infrared.

“The sensitivity of the Herschel observations enables us to see not only the glow from dust in and around the galaxy, but also emission from electrons in the jets spiraling in magnetic fields at velocities close to the speed of light,” said Göran Pilbratt from ESA.

ESA’s XMM-Newton X-ray observatory recorded the high-energy glow from one of the jets, extending more than 12,000 light-years away from the galaxy’s bright nucleus.

XMM-Newton’s X-ray view shows not only the way that the jet interacts with the surrounding interstellar matter, but also the galaxy’s intensely active nucleus and its large gaseous halo.

“XMM-Newton is well-suited to detecting extended weak X-ray emission, often allowing us to see halos around galaxies for the first time,” said Norbert Schartel from ESA.

The jets seen by both satellites are evidence of the supermassive black hole — 10 million times the mass of our Sun — at the center of the galaxy.

This unique collaboration, alongside observations from the ground in visible light, has given us a new perspective on the drama in objects like Centaurus A, with a black hole, star birth, and the clashing of two distinct galaxies all rolled into one.