A major eruption from a supermassive black hole

Diagram of coronal eruption. At the left the corona (feature in purplish colors) gathers inward, becoming brighter, before shooting away from the black hole (middle and right) (Image NASA/JPL-Caltech)
Diagram of coronal eruption. At the left the corona (featured in purplish colors) gathers inward, becoming brighter, before shooting away from the black hole (middle and right) (Image NASA/JPL-Caltech)

An article published in the journal “Monthly Notices of the Royal Astronomical Society” describes the detailed observation of a huge X-ray eruption by a supermassive black hole known as Markarian 335 or Mrk 335. The Swift and NuSTAR space telescopes were used to examine this phenomenon of gigantic proportions concluding that it originated from a coronal ejection.

By their nature, black holes don’t emit light but are surrounded by disks of dust and gas that can become very bright if their temperature gets high enough. In the case of supermassive black holes, which can have a mass even billions of times the Sun, the gravitational effects of those masses shrank into tiny volumes can make those disks incandescent.

In the vicinity of the black hole there is the corona, a structure composed of particles heated to such a level that ends up emitting X-rays. There are two models for the corona’s configuration. According to the “lamppost” model, these structures are compact light sources, similar to bulbs, placed above and below the black hole, along its rotation axis. According to another model, the corona is distributed in a more diffuse manner in space, like a giant cloud around the black hole or as a “sandwich” around the disk of material like slices of bread. A corona can also switch from one configuration to the other.

Markarian 335 is a supermassive black hole about 324 million light years from Earth already the subject of study because it has an interesting history. It was once one of the brightest X-ray sources but in 2007 its brightness greatly diminished. Dirk Grupe of Morehead State University in Kentucky, one of the authors of this research, started keeping an eye on it with the Swift space telescope to try to understand what happened.

In the following years, Markarian 335 had several eruptions and in September 2014 one of them was particularly powerful. On that occasion, Louis Gallo, another of the authors of this research, managed to obtain an observation of the phenomenon with the NuSTAR space telescope, launched in 2012 exactly to observe high-energy X-ray sources.

By analyzing the X-ray spectrum over a range of wavelengths observed by both Swift and NuSTAR, the researchers were able to verify that the corona had moved. In fact, it emitted X-rays with a spectrum a bit different from that of the accretion disk. Put simply, the corona had an increase of brightness at X-rays due to its displacement.

The corona move very fast: 20% of that of light, equal to about 60,000 km/s (almost 37,300 mps). The movement direction creates a relativistic effect called in jargon Doppler boosting with the result that the brightness increases when the corona moves towards the observer.

The energetic source of X-rays at the base of these coronal ejections still needs to be understood. The combined use of the Swift and NuSTAR space telescopes allowed to make observations better than the past providing new information on this phenomenon. Astronomers are ready for the next eruptions to try to understand these enormous energy emissions.



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