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The universe contains an amazing variety of galaxies,
but when it comes to their colors, there are generally just two categories:
distinctly blue, or distinctly red.
The blue ones are actively forming new stars, so are more “alive.”
In fact, it’s the characteristic blue shine of a baby star that gives these galaxies their
color.
On the other hand, red galaxies are considered “dead.”
They’re not forming new stars; they’re usually blobs that are kind of just sitting
there.
But what about galaxies in the middle?
Ones that are in the process of dying?
Well, astronomers haven’t seen or gotten a good look at many of those.
At least, until now.
In a paper published on Monday in the journal Nature Astronomy
, researchers described observations of a galaxy called ID2299.
Its light has taken nine billion years to get to us,
but from our perspective,
it seems to be in the midst of its death spiral.
And the reason why it’s dying is not at all what we expected.
To understand galactic death,
it helps to know a little about star formation, too.
New stars form when massive regions of cold gas located within galaxies collapse.
And in theory, galaxies can keep forming stars until they exhaust their gas supply.
But... that doesn’t seem to happen in reality.
If it did, scientists would see galaxies in all stages of star formation,
including many in the “dying” phase between red and blue.
Instead, they see galaxies making stars efficiently
until they just suddenly stop.
It’s called quenching.
And it happens because the galaxy’s gas is thrown into intergalactic space,
dispersing too much to form stars.
For a long time, astronomers thought gas was being blown away by powerful interstellar
winds — maybe ones made by star formation itself, or by a powerful supermassive black
hole.
But when the paper’s authors used the ALMA radio telescope to study ID2299,
they found a totally different situation.
This galaxy’s cold gas looked like it was being ejected not because of interstellar
wind,
but because of a collision.
It turns out that ID2299 seems to be the product of two galaxies merging.
And as they come together,
all those intense gravitational interactions are creating something called a tidal tail:
a long stream of stars and gas stretching from ID2299 into interstellar space.
And that tail is carrying away an eye-watering amount of matter:
The galaxy is losing about half its gas
A hit like that is likely to deal a crushing blow to any ongoing star formation —
the exact quenching effect astronomers have known about for years.
So, is a violent collision how all galaxies die?
Probably not.
Instead, it’s likely just a new weapon in nature’s arsenal.
This galaxy wasn’t the only unusual thing making headlines this week, though.
In a paper published in the Astrophysical Journal Letters,
a pair of researchers described new observations of one of the universe’s most unique objects.
It’s called J1818 for short, and it’s a neutron star that is just, well, the most.
For starters,
neutron stars are extreme all by themselves.
They’re the collapsed cores of stars that have gone supernova and died.
And they’re typically 10 to 20 kilometers across,
but contain twice as much mass as the Sun.
All that mass creates a pressure so high
that most of the star’s protons and electrons are literally crammed
into one another until they become neutrons.
Hence the name.
But J1818 isn’t just a neutron star.
It also falls into two other, special categories:
It’s a magnetar, and it’s a pulsar.
Magnetars are neutron stars with incredibly powerful magnetic fields —
the strongest ones of any object in the universe.
Meanwhile, pulsars are a little different.
They’re not always neutron stars.
Generally, they’re objects that spin and blast out beams of light,
which sweep around like a lighthouse.
As the beam sweeps over Earth, the object appears to pulse or flash.
In this case, J1818 appears to pulse with bursts of radio waves.
Now, there are plenty of pulsars out there,
but J1818 is only the fifth object known to be both a pulsar and a magnetar.
And it’s probably the youngest of the bunch!
It appears to be less than 500 years old.
So in their study, the research team looked for any remnant of the supernova explosion
that would have formed it.
They found what looks like a promising candidate,
but there’s one catch:
J1818 seems way too far away from the center of the explosion.
For it to have traveled that far, it would need to be going absurdly fast.
Like, even if it were 5000 years old instead of 500,
it would still need to be going more than one percent the speed of light,
or almost 13 million kilometers per hour.
That’s way faster than any known neutron star.
But, hey, this thing seems to be over-the-top in every other way,
so maybe we shouldn’t count it out just yet.
Because if there’s any unifying theme between these two studies,
it’s that objects in space often exceed our expectations.
Thanks for watching this episode of SciShow Space!
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