This illustration shows SS 433, a black hole or neutron star, as it pulls material away from its companion star. The stellar material forms a disk around SS 433, and some of the material is ejected into space in the form of two thin jets (pink) traveling in opposite directions away from SS 433. Credit: DESY/Science Communication Lab
Known as ultraluminous X-ray sources, the emitters are easy to spot when viewed straight on, but they might be hidden from view if they point even slightly away from Earth.
It’s hard to miss a flashlight beam pointed straight at you. But that beam viewed from the side appears significantly dimmer. The same holds true for some cosmic objects: Like a flashlight, they radiate primarily in one direction, and they look dramatically different depending on whether the beam points away from Earth (and nearby space telescopes) or straight at it.
New data from
This animation illustrates how SS 433 — which contains a bright light source surrounded by two bowl-shaped structures — tilts back and forth in its orbit. As with a flashlight, the light of SS 433 appears much dimmer when viewed from the side. Credit: NASA/JPL-Caltech
The new study shows that the object known as SS 433, located in the
The cosmic object SS 433 contains a bright source of X-ray light surrounded by two hemispheres of hot gas. SS 433 tilts periodically, causing one X-ray beam to point toward Earth. Credit: NASA/JPL-Caltech
“It’s been known for a long time that this thing is eating at a phenomenal rate,” said Middleton. “This is what sets ULXs apart from other objects, and it’s likely the root cause of the copious amounts of X-rays we see from them.”
The object in SS 433 has eyes bigger than its stomach: It’s stealing more material than it can consume. Some of the excess material gets blown off the disk and forms two hemispheres on opposite sides of the disk. Within each one is a cone-shaped void that opens up into space. These are the cones that corral the high-energy X-ray light into a beam. Anyone looking straight down one of the cones would see an obvious ULX. Though composed only of gas, the cones are so thick and massive that they act like lead paneling in an X-ray screening room and block X-rays from passing through them out to the side.
Scientists have suspected that some ULXs might be hidden from view for this reason. SS 433 provided a unique chance to test this idea because, like a top, it wobbles on its axis – a process astronomers call precession.
Illustration of the NuSTAR spacecraft, which has a 30-foot (10 meter) mast that separate the optics modules (right) from the detectors in the focal plane (left). This separation is necessary for the method used to detect X-rays. Credit: NASA/JPL-Caltech
Most of the time, both of SS 433’s cones point well away from Earth. But because of the way SS 433 precesses, one cone periodically tilts slightly toward Earth, so scientists can see a little bit of the X-ray light coming out of the top of the cone. In the new study, the scientists looked at how the X-rays seen by NuSTAR change as SS 433 moves. They show that if the cone continued to tilt toward Earth so that scientists could peer straight down it, they would see enough X-ray light to officially call SS 433 a ULX.
Black holes that feed at extreme rates have shaped the history of our universe. Supermassive black holes, which are millions to billions of times the mass of the Sun, can profoundly affect their host galaxy when they feed. Early in the universe’s history, some of these massive black holes may have fed as fast as SS 433, releasing huge amounts of radiation that reshaped local environments. Outflows (like the cones in SS 433) redistributed matter that could eventually form stars and other objects.
But because these quickly consuming behemoths reside in incredibly distant galaxies (the one at the heart of the Milky Way isn’t currently eating much), they remain difficult to study. With SS 433, scientists have found a miniature example of this process, much closer to home and much easier to study, and NuSTAR has provided new insights into the activity occurring there.
“When we launched NuSTAR, I don’t think anyone expected that ULXs would be such a rich area of research for us,” said Fiona Harrison, principal investigator for NuSTAR and a professor of physics at Caltech in Pasadena, California. “But NuSTAR is unique in that it can see almost the whole range of X-ray wavelengths emitted by these objects, and that gives us insight into the extreme processes that must be driving them.”
Reference: “NuSTAR reveals the hidden nature of SS433” by M J Middleton, D J Walton, W Alston, T Dauser, S Eikenberry, Y-F Jiang, A C Fabian, F Fuerst, M Brightman, H Marshall, M Parker, C Pinto, F A Harrison, M Bachetti, D Altamirano, A J Bird, G Perez, J Miller-Jones, P Charles, S Boggs, F Christensen, W Craig, K Forster, B Grefenstette, C Hailey, K Madsen, D Stern and W Zhang, 6 May 2021, Monthly Notices of the Royal Astronomical Society. DOI: 10.1093/mnras/stab1280
More About the Mission
NuSTAR is a Small Explorer mission led by Caltech and managed by NASA’s Jet Propulsion Laboratory, a division of Caltech, for the agency’s Science Mission Directorate in Washington. NuSTAR was developed in partnership with the Danish Technical University and the Italian Space Agency (ASI). The spacecraft was built by Orbital Sciences Corporation in Dulles, Virginia (now part of Northrop Grumman). NuSTAR’s mission operations center is at the (function(d, s, id){
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