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Seeing giant things smash into each other
is one of the great pleasures of astronomy.
So it’s no surprise that astronomers were
excited to announce
that they’ve seen a collision between two
of the universe’s most extreme objects
for the first time: a black hole and a neutron
star.
Even cooler, this observation was made not
with light,
but with ripples in the fabric of space-time
called gravitational waves.
Black holes and neutron stars are the remnants
of giant stars
that have undergone a supernova explosion.
If the dying star has a core with a mass roughly
two to three times larger than our Sun
it ends up as a neutron star --
an incredibly dense body made mostly of neutrons.
Stars bigger than that collapse all the way
down to a black hole.
Large stars often form in binary pairs.
And since those big stars will eventually
die,
it’s not too surprising to see black holes
and neutron stars orbiting each other.
In the past, astronomers have seen black holes
collide with other black holes
and even two neutron stars hit one another.
But these latest observations mark the first
time an object of each type
has been involved in the collision.
The event was detected by LIGO and VIRGO,
gravitational wave observatories located in
the United States and Italy.
Gravitational waves work kind of like someone
sitting down on the couch next to you.
You don’t have to see it happen
because you can feel how their weight distorts
the cushions.
Einstein’s theory of general relativity
says
that gravity distorts the fabric of the universe
in much the same way.
Because neutron stars and black holes both
have a ton of gravity,
their collision sends out a massive disturbance
that can travel an incredible distance --
in this case, around 900 million light-years.
LIGO and VIRGO detect these gravitational
waves using a technique called interferometry,
which combines a pair of lasers pointed at
right angles to one another.
When a gravitational wave washes over the
detector,
it makes space literally shorter in one direction
and longer in the other.
The two lasers thus travel different distances,
causing a change in travel time that records
the presence of the wave.
This all sounds kind of straightforward,
but getting it to actually work was so difficult
that it almost immediately scored a Nobel
Prize back in 2017.
By combining multiple detectors,
scientists can filter out any false positives
and triangulate where the event must have
taken place.
Seeing the merger between these two kinds
of objects isn’t just a nifty addition
to our collection of cool space collisions.
Astronomers hope by analyzing how the black
hole ripped the neutron star apart,
they can improve their understanding of the
structure of neutron stars,
and how resilient they are.
Closer to home,
this month NASA has announced that its upcoming
Europa Clipper mission
has taken an important step forward.
The project, which will probably cost about
four billion dollars,
has moved from a preliminary draft to its
final design stage.
Its goal is to study Jupiter’s moon Europa,
which planetary scientists believe conceals
a vast ocean of liquid water under its icy
surface.
All that water makes Europa perhaps the very
best place in the solar system to search for
extraterrestrial life.
Although the mission is moving into the next
phase of planning,
it hasn’t been entirely smooth sailing for
the Clipper thus far.
NASA announced back in March 2019
that it was cancelling development of a key
instrument
designed to measure the depth of Europa’s
hidden ocean.
The device, called a magnetometer,
would have precisely measured the magnetic
fields created by currents of electricity
within the ocean.
But tests showed that the sensor,
which was already three times over-budget,
would have struggled to handle the intense
radiation environment around Jupiter.
Instead NASA will replace the specially designed
magnetometer
with a more generic type used on other missions.
This off-the-shelf part will be more reliable,
but less precise:
instead of measuring the ocean’s depth to
within 20 kilometers,
it could be off by as much as a hundred.
And, if the ocean is particularly conductive
to electricity,
the sensor may not return much information
at all.
That’s not ideal,
but eliminating mission components that threaten
the progress of the overall project
is a key element in the design review process.
There’s also uncertainty about how the spacecraft
will actually get to Jupiter.
While Congress has mandated that the Europa
Clipper fly aboard NASA’s upcoming Space
Launch System,
that rocket won’t even be available until
years after the satellite itself is ready
in 2023.
The mission could instead launch on schedule
aboard a commercial rocket like the Falcon
Heavy for a fraction of the price,
but the trip would be slower and require a
tricky flyby of Venus along the way.
Still, these kinds of uncertainties are normal
for a mission as complex
and ambitious as the Europa Clipper.
The fact that NASA has given mission planners
the green light to move ahead
is a big deal and takes us one step closer
to exploring yet another new place in the
solar system.
Thanks for watching this episode of SciShow
Space News!
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