In late August, an instrument on the International Space Station, called NICER, spotted its brightest burst of X-ray radiation yet.
NICER, or the Neutron Star Interior Composition Explorer, studies X-rays that come from neutron stars, the super-dense remnants of some stars after they go supernova. This particular burst came from a neutron star called SAX J1808. The burst was extremely energetic, releasing about as much energy in 20 seconds as the sun does in 10 days.
SAX J1808 is partnered with a brown dwarf (an object somewhere between a star and a gas giant planet). The neutron star pulls hydrogen gas from the companion object into a swirling disk around it. These gases can also fall inward from disk to neutron star, sometimes triggering explosions that detectors like NICER see as bursts of X-rays.
Whats special about this burst?
Astronomers saw evidence that the explosion blew material off of the neutron star in two layers. A layer of hydrogen was likely ejected first, followed by a layer of helium. NICER had previously seen neutron stars give off X-ray bursts that corresponded to either hydrogen or helium layers, but not both in a single burst like this.