Astronomers found a peculiar alignment of novae explosions with a massive jet in the M87 galaxy. Despite various theories, the exact reason for this alignment remains a mystery.
Everyone loves a good mystery, and astronomers have just uncovered a new one in a nearby supermassive galaxy called M87. Like most galaxies, M87 regularly plays host to a smattering of stellar explosions called novae, each the result of a star stealing material from a neighbor. M87 also features a massive jet of
These phenomena: the jet and the novae, are unrelated astronomical occurrences, or so scientists believed. But astronomers recently discovered that the novae in M87 seem to be uncharacteristically aligned along the jet, instead of scattered randomly throughout the galaxy. Is the jet somehow triggering nova explosions?
It might be, but the mystery is: how?
Recent Findings and Theories
Using data from two separate surveys by the
Understanding Novae and Galactic Jets
Here’s what we know so far. Novae are caused by explosions from the surface of white-dwarf stars. For a nova to occur, the
Meanwhile, M87’s galactic jet is driven by the
Challenging Theories
There are a couple of theories as to how the jet might set off novae.
One simple explanation is that radiation from the jet is heating donor stars in its path, increasing mass transfer to their white dwarf partners and triggering a thermonuclear runaway. Such heating would make novae more frequent.
Unfortunately, the math on this theory doesn’t check out. As powerful as the radiation from the jet is, the stars are too small and the distances too great for it to have much influence. We can probably rule this answer out: the effect is “orders of magnitude” too weak.
Another suggestion is that the jet is triggering star formation: more stars means more binaries, which means more novae. But there’s a problem with this explanation too. In this scenario, you would also expect to see a similar increase in star formation along the galaxy’s ‘counterjet’, and that isn’t borne out by the evidence.
So astronomers are going back to the drawing board.
Emerging Hypotheses
There are a couple of other ideas they are considering but have not yet properly tested. Perhaps, for example, the jet’s shock waves are shepherding gas and dust together as it moves through the galaxy, forming clouds of interstellar medium. As one of these clouds arrives at a binary star system, it would increase the rate of material accretion, setting off a nova. Similarly, a shock wave might also heat a star up (more effectively than radiation could on its own), increasing the mass transfer rate.
These last two possibilities are as-of-yet just guesses: they haven’t yet been fully explored.
So for now, it remains a mystery.
In the words of the authors, “the enhanced rate of novae along M87’s jet is now firmly established, and unexplained.”
Adapted from an article originally published on Universe Today.
Reference: “A 9-Month Hubble Space Telescope Near-UV Survey of M87. II. A Strongly Enhanced Nova Rate near the Jet of M87” by Alec M. Lessing, Michael M. Shara, Rebekah Hounsell, Shifra Mandel, Nava Feder and William Sparks, 28 September 2023, Astrophysics > High Energy Astrophysical Phenomena.
arXiv:2309.16856