- 4198 - M87 GALAXY - why is it a mystery? M87’s galactic jet is driven by the black hole at the center of the galaxy. This was the first black hole ever imaged by astronomers in 2019. As material spirals in towards the back hole, an accretion disk forms around it, and powerful magnetic fields funnel intense radiation outward, causing it to be expelled at relativistic speeds, traveling almost 5,000 light years out into deep space.
--------------------- 4198 - M87 GALAXY - why is it a mystery?
- Astronomers have
just uncovered a new mystery 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 features a
massive jet of plasma blasting out into deep space from the galactic core.
These jets and the novae, were thought to be unrelated astronomical
occurrences. But, astronomers recently discovered that the novae in M87 seem to
be aligned along the jet, instead of scattered randomly throughout the galaxy.
Is the jet somehow triggering nova explosions?
-
- Using data from two
separate surveys by the Hubble Space Telescope, astronomers confirmed the
presence of 135 novae within M87, and they appear to occur with unexpected
frequency in the path of the jet.
-
- No other galaxy
with jets has been observed with sufficient sensitivity or frequency to yield
samples of novae large enough to check if M87’s putative nova-jet connection is
ubiquitous, rare or spurious.
-
- Novae are caused
by explosions from the surface of white-dwarf stars. For a nova to occur, the
white dwarf must be in a binary pair, and be close enough to its partner star
to accret material from it. Unlike a supernova, a nova doesn’t completely
destroy the white dwarf, and the same star can have multiple novae occur over
time as more and more material is stolen from its partner.
-
- M87’s galactic jet
is driven by the black hole at the center of the galaxy. This was the first black hole ever imaged by
astronomers in 2019. As material spirals in towards the back hole, an accretion
disk forms around it, and powerful magnetic fields funnel intense radiation
outward, causing it to be expelled at relativistic speeds, traveling almost
5,000 light years out into deep space.
-
- 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.
-
- 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 because 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 ‘counter jet’, and that isn’t born out by the
evidence.
-
- There are a couple
of other ideas they are considering but have not yet properly tested. Perhaps
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.
-
- A shock wave might
also heat a star up (more effectively than radiation could on its own),
increasing the mass transfer rate.
-
- So for now, it
remains a mystery. I'm working on
it.
-
-
October 24, 2023 M87
GALAXY - why is it a mystery? 4197
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