A star that keeps mimicking its own explosion has a hidden black hole or neutron star partner, study finds

Astronomers have found what keeps setting off a giant star in NGC 4559, a spiral galaxy about 30 million light-years from Earth, that flares like an exploding star about three times a year yet never dies:  a hidden partner, either a black hole or a neutron star, that pulls gas off it each time the two swing close, a study published Monday in The Astrophysical Journal reports.  A robotic telescope on Mount Hamilton, east of San Jose, helped time the observations.

What the star is

The star, AT 2016blu, sits near the outer edge of NGC 4559, NASA says. The galaxy’s distance, about 30 million light-years, is roughly 176 quintillion miles by our arithmetic, so the light reaching Earth now left it about 30 million years ago.  It has at least 33 times the sun's mass.  It is a luminous blue variable, a hot, heavy kind of star whose brightness swings widely.  Its flare-ups are so strong they resemble supernovas, the explosions that destroy massive stars, but because it survives, astronomers call it a supernova impostor.  Telescopes recorded 27 outbursts between 2012 and June 2026, one about every 113 days.

How they caught the partner

The team suspected X-rays, high-energy light our eyes can't see, were powering the flashes.  So astronomers watched the star in ordinary light, and when it began brightening in early 2026 they triggered NASA's Chandra X-ray Observatory, a space telescope launched in 1999, to look during the outburst.  Chandra's views over several days in March 2026 showed the star at least 100 times brighter in X-rays than in Chandra images from 2001 and 2002, before the outbursts began.

The researchers' explanation:  the pair travel an oval orbit.  At closest approach, gas thrown off by the big star falls onto the small, dense partner, whirls around it at close to the speed of light and gets hot enough to glow in X-rays.  That X-ray glow alone is roughly 100,000 times the sun's total energy output, by our arithmetic from the paper's figures.  It is the first X-ray detection of this kind of erupting star and the first found with a black hole or neutron star partner, Chandra's Nov. 9 announcement says.  The team hasn't yet determined which of the two the partner is.

The Mount Hamilton connection

Part of the watch in ordinary light came from the Katzman Automatic Imaging Telescope, or KAIT, a 30-inch robotic telescope at the University of California's Lick Observatory, which sits at about 4,200 feet on Mount Hamilton, more than 20 miles from downtown San Jose.  KAIT opens its own dome on clear nights and searches for exploding stars with no human operator.  It cost about $500,000, mostly from the National Science Foundation, the observatory says.  UC Berkeley astronomer Alex Filippenko, who designed KAIT, is a co-author, and more than 30 amateur astronomers also tracked the star's brightness.

Why it matters

The finding may tie supernova impostors to ultraluminous X-ray sources, rare, very bright X-ray objects astronomers don't fully understand, and may help explain why some massive stars flicker before they finally explode.  It comes from one team's peer-reviewed study and hasn't been independently confirmed.  The star is far too faint to see from San Jose without a large telescope.

Source:  Aghakhanloo et al., "AT 2016blu: Accretion-powered Outbursts in a Luminous Blue Variable and Compact Object Binary", The Astrophysical Journal 1011:252 (Nov. 9, 2026, CC BY 4.0); NASA Science, "NASA's Chandra Finds Source of Star's Mysterious Outbursts" (Nov. 9, 2026) and Chandra mission page; Lick Observatory, "Katzman Automatic Imaging Telescope (KAIT)" and "Visit".  Distance in miles and the comparison with the sun are the Daily News's own arithmetic.  Drafted by AI for San Jose using NASA source material.  NASA did not write or review this story.