Data From NASA NuSTAR Reveals Importance of Perspective; More Undetected Ultraluminous X-ray Source Possible

New data from the NASA Nuclear Spectroscopic Telescope Array (NuSTAR) space observatory show that some of the universe's brightest objects, the ultraluminous X-ray sources (ULX), might be virtually invisible if they are pointed somewhere else.

The phenomenon is best explained by any focused light source, like a flashlight, that is easily detected when pointed directly at someone. Otherwise, these objects are less brighter when viewed sideways. According to the latest observations from the NASA NuStar observatory, ULX might be the same.

Researchers present their findings in the report "NuSTAR Reveals the Hidden Nature of SS433," published in the Monthly Notices of the Royal Astronomical Society.

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Ultraluminous X-Ray Sources Across the Galaxy

While many objects emit light across the universe, most of them give off very little in the X-ray spectrum, especially in the high-energy range detectable by the NuSTAR. On the other hand, ultraluminous X-ray sources radiate very brightly across the X-ray darkness.

A cosmic X-ray source is considered a ULX if its emission is about a million times brighter compared to the total light output of the Sun across all wavelengths, according to the NASA Jet Propulsion Laboratory. Their X-ray luminosity is so high that they can even be detected from other galaxies millions of light-years away.

Researchers made the ULX observation after examining an object designated as SS433, located in the Milky Way some 20,000 light-years from Earth. Despite being 1,000 times dimmer than current thresholds for qualifying ultraluminous X-ray sources, researchers define it as such.

However, this faint luminosity is not absolute but relative as SS433 emits its bright X-ray lights in two gaseous cones on both sides of the source. These 'cones' in turn confines the emission of the ULX, with a thin disk of emissions from the center being the signals captured by NuSTAR.

Seeing how SS433 behaves, researchers believe that there may be ultraluminous X-ray sources, especially from other galaxies, that are not yet detected by the NuSTAR because of the same circumstances. This suggests that the number of ULX in existence is higher than initially believed.

Luminosity Based on Orientation and Perspective

So far, there are about 500 ULX found in other galaxies millions of light-years away from Earth, according to SciTech Daily.

This distance also makes it virtually impossible to determine the source of these ultraluminous X-ray emissions. They could either be a neutron star, the remains of a collapsed supergiant star, or a black hole no more than 30 times as massive as our own Sun.

Both objects can generate X-rays from gases subjected to extreme temperatures as they interact with very dense objects.

For the case of SS433, astronomers behind the latest study are looking at the possibility of a black hole ten times more massive than our Sun.

Another significant observation is that the ULX, or the object that creates it, is starting to eat away at a nearby star. SS433 siphons a lot of material, about 30 Earth masses, from its neighbor star in a single Earth year.