New ultraluminous X-ray source detected in galaxy NGC 55

Tomasz Nowakowski is a member of the physics.org community.

An international team of astronomer have observed a nearby galaxy using two telescopes. A new ultraluminous X-ray source has been found. There is a paper on the arXiv pre-print server.

Each point source in the sky that emits more radiation than 1 million suns emits more X-rays. They are more Luminous than any known stellar process. Many studies of ULXs have been done, but the basic nature of these sources is still unknown.

One of the closest galaxies to the Local Group is called The WhaleGalaxy. It's mass is estimated to be 20 billion solar mass. At least one ULX has been found in previous observations of NGC 55 with X MM-Newton.

There is a group of astronomer led by the University of Palermo in Italy. They were able to reclassify the object as a ULX because it reached a luminosity peak.

The researchers wrote in the paper that they provided evidence for a new ULX in the galaxy.

Robba's team was able to find a luminosity peak higher than 1.6 duodecillion erg/s with new deeper X MM-Newton observations. The source was confirmed as a ULX and given a designation.

The Transient nature of some ULXs makes them not always new sources. Some sources can be detected with less than 1 duodecillion erg/s before they reach the ULX regime.

The study found that the soft spectrum is different from the hard spectrum. The X-ray spectrum of ULX-2 was classified as a soft ULX by the astronomer.

The time scales of the flux variations are of the order of a month. It is most likely caused by small changes in the accretion rate or by super-orbital modulations.

The astronomer searched for periodic signals from the ULX-2. No significant signals were found from this source.

More information: A. Robba et al, A transient ultraluminous X-ray source in NGC 55. arXiv:2207.09447v1 [astro-ph.HE], arxiv.org/abs/2207.09447

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