[♪ INTRO] Astronomers
are constantly searching the night sky for
evidence of new and amazing things in the universe.
Like a flash of light, a burst of particles, or a ripple in the fabric of space.
But sometimes, the most remarkable finding is… nothing at all.
In fact, recently, an especially surprising bit of nothing was the key to
helping astronomers realize that they were looking at something they had
never seen before: a planet that had survived its star’s destruction intact.
This week, in the journal Nature, astronomers published their discovery of a planet
the size of Jupiter orbiting the remains of a star that was once like the Sun.
Now, before these astronomers zeroed in on this particular “nothing”
that led to this discovery, they did see something.
Back in 2010, researchers saw an ordinary star suddenly brighten.
That can happen for a few reasons, but in this case,
it was caused by an effect called gravitational lensing.
Gravitational lensing happens because of the way mass bends space.
As light passes through the warped space around a massive object, it curves.
And if things line up just right, that light can be focused toward Earth
just like how a glasses lens focuses light towards your eye.
The sudden brightening of the star astronomers observed in 2010 was caused by
a small gravitational lens, known as a microlens, created by an unknown object.
It was focusing the star’s light toward Earth as the two objects lined up.
But in 2015, astronomers turned the powerful Keck telescope to this spot in the sky…
and where the lensing object should have been, they found nothing.
The same thing happened in 2016 and 2018. That was odd, considering the object
was only 6500 light-years away, which was well within Keck’s range.
So the fact that astronomers saw nothing meant that
whatever was out there was extremely dim. Way too dim to be any ordinary star.
Various aspects of the gravitational lens ruled out the possibility that it was
a remnant of a massive star, like a neutron star or a black hole.
So that left the team with just one conclusion: The main lens had to be
a white dwarf, a dense, cool star that is the ultimate fate of stars like our Sun.
Along with this finding, there was one unusual detail that drew researchers’ attention.
The shape of the lens had some abnormalities. And they pointed to the presence of
a Jupiter-sized planet orbiting it at a distance a few times larger than
Earth’s orbit around the Sun. Which leaves one big question:
How in the world did that planet survive? The process of going from an ordinary star like
the Sun to a white dwarf is a violent one. At the end of its life, a Sun-like star
puffs up to 100 times its original size. Then, it throws off its outer layers of gas,
which flow outward like a cosmic mop, sweeping aside anything in their path,
and leaving behind a hot, dense core. The researchers don’t speculate
as to how this planet survived. But it had to have been a wild ride.
In other surprising news, an article published last month in the journal
Physical Review D suggests that experiments designed to
detect dark matter might actually be capable of detecting dark energy, too.
This is stranger than it sounds, because, despite their similar names,
dark matter and dark energy are basically opposites.
Dark matter is the unseen source of gravity that seems to
hold together the galaxies, while dark energy is the
unknown force that is pushing the universe apart. But, because dark matter and dark energy remain
basically unknown, there are a bunch
of competing hypotheses to explain each. And some of them center on hypothetical particles
that happen to have similar properties. This paper in particular is trying to
explain some unexplained detections made by a dark matter detection experiment
that ran in Italy between 2016 and 2018. The observations it made aren’t easily
explained by any of the existing dark matter hypotheses, so the researchers
went looking for another explanation. And they came up with a hypothesis based on
so-called chameleon particles. Unlike ordinary particles,
hypothetical chameleon particles have different properties in different places.
In the past, theorists have invoked them as a way to
explain what dark energy’s physical form might be like.
The hypothesis is that, around other matter, chameleon particles have
a lot of mass, but interact with other matter very weakly.
Then when they’re on their own, their mass drops to almost nothing,
while their interactions grow much stronger. If that sounds super weird, it is,
but that’s kind of the point. Dark energy seems totally unlike
anything else in the cosmos. The research team simulated the
effects that a stream of chameleon particles emanating from the Sun would have on the
Italian dark matter experiment, and found a surprisingly close
match to what was actually observed. Now, that’s hardly a definitive statement, and,
in fact, the statistical significance of it is far less than what is generally accepted in
particle physics. But it is an
eye-opening idea, and one that may cause future detection experiments to consider a
wider range of possible targets. After all, if you’re designing an
experiment to look for something that’s almost totally unknown, you might as well cast a wide net
and see what else you can find! Thanks for watching this episode
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