Astronomers have spotted a variety of weirdly blinking phenomena out there in the big wide Milky Way through history, but a newly discovered pulsating object truly appears to be one of a kind.
Located several thousand light-years away, the object named CHIME J1634+44 is a rare case of a cosmic light that brightens and fades over inexplicably long timescales. A mere dozen or so of these so-called long-period transients (LPTs) have been discovered in the galaxy to date… but CHIME J1634+44 is truly in a league of its own.
Whatever the object is, it has the most polarized light ever seen from an LPT, suggesting it is nestled within a rather complicated environment. Moreover, the timing between its flashes of radio waves seems to be growing shorter rather than longer, suggesting that rather than slowing down as space objects typically do, the spin of CHIME J1634+44 is speeding up.
Then there’s the period itself. Or rather periods. There are two.
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“You could call CHIME J1634+44 a ‘unicorn’, even among other LPTs,” says astronomer Fengqiu Adam Dong of Green Bank Observatory, first author on one of two papers describing the mystery object.
“The bursts seem to repeat either every 14 minutes, or 841 seconds – but there is a distinct secondary period of 4206 seconds, or 70 minutes, which is exactly five times longer. We think both are real, and this is likely a system with something orbiting a neutron star.”
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Both teams releasing papers detected the object independently, using different sets of data. Both teams found the same spin-up, the same pair of periodicities, and the same polarization. The second paper was led by astronomer Sanne Bloot of the Netherlands Institute for Radio Astronomy.
When we detect something in space behaving in a very strange manner, there are a fairly limited number of things we know it can be, depending on the way it’s behaving. So far, all the evidence we have on LPTs suggests that they are compact objects – that is, white dwarfs or neutron stars.
Both are left after stars of a certain mass range die, their outer material ejected, and their core – no longer supported by the outward pressure supplied by fusion – collapsing under gravity to form a highly compact object.
The least massive of the two are white dwarfs. They are up to around 1.4 times the mass of the Sun packed into a sphere between the diameters of Earth and the Moon. The only thing that keeps them from collapsing further is a rule that states electrons can’t occupy the same quantum state, resulting in a resistance referred to as electron degeneracy pressure.
Electron degeneracy pressure fails for objects with more mass, squishing some 2.3 Suns worth of mass into a sphere about 20 kilometers (12 miles) across. Supported instead by neutron degeneracy pressure, they are called neutron stars.
Because neutron stars are so dense, they can do some pretty wacky things to the space around them, especially if they have a binary companion.
Both papers conclude that this is what’s probably going on with CHIME J1634+44. If one of the objects is actively slurping up material from a closely-orbiting companion, the accumulation of mass could be causing its spin rate to accelerate. What is unclear is whether that star is a white dwarf or a neutron star.
Dong and his colleagues think it is more likely to be a neutron star, perhaps a pulsar, since pulsars emit periodic pulses of radio waves, and are known, sometimes, to increase their spin rate.
However, Bloot and her colleagues believe that the object is a white dwarf. They found a faint ultraviolet source at the location of CHIME J1634+44 that is consistent with a white dwarf star around 78 percent of the mass of the Sun, with an effective temperature between 15,000 and 33,000 Kelvin.
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If this is the case, then the object could be a white dwarf pulsar – and elusive, rarely seen type of object that behaves similarly to its neutron star analogue.
It’s going to take more observations to determine if this is the case, but scientists will want to take a closer look anyway. Remember that polarization signal? It’s perfectly circular, and we’ve never seen that in an LPT before. This could mean that the radio pulses from CHIME J1634+44 are produced in a manner never seen before.
So, as astronomers like to say: watch this space.
“The discovery of CHIME J1634+44 expands the known population of LPTs and challenges existing models of neutron stars and white dwarfs,” Dong says, “suggesting there may be many more such objects awaiting discovery.”
Dong’s team’s paper has been published in The Astrophysical Journal Letters. Bloot’s team’s paper has been accepted into Astronomy & Astrophysics, and is available on arXiv.
