All the time, NASA is developing new technologies that will help us unravel
the mysteries of the universe. Despite its uniformity, the cosmos remains an explosive
and wildly unpredictable place, full of things we can’t yet understand. But one day, we will, and
that’s thanks to humanity’s constant ingenuity. This is Unveiled, and today we’re answering the
extraordinary question: why is NASA exploring the universe’s most dramatic objects?
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In December 2021, NASA launched the Imaging X-Ray Polarimetry Explorer, a space observatory with a
huge mandate: to study some of the weirdest, most complex, and dangerous celestial bodies
in the universe. Called IXPE for short, the craft is one satellite of many that NASA has designed
to study astrophysical phenomena in the wider universe. In its sights, IXPE has everything
from black holes to quasars to magnetars - truly the biggest, most powerful, and most
“dramatic” objects that exist in outer space. IXPE can study them because it’s able to image the
X-rays that these objects produce, which other kinds of telescopes are incapable of seeing.
Not only are X-rays invisible to other telescopes, they’re invisible to humans as well;
our eyes can’t see X-rays, because they’re beyond the visible light spectrum. IXPE is
necessary over other more famous telescopes like James Webb, launched the same month,
because it’s an infrared telescope looking at the other end of the electromagnetic spectrum.
The Hubble Space Telescope doesn’t look at the X-ray region of the spectrum either. IXPE is,
however, not the only X-ray telescope NASA has. It also has the Chandra X-Ray Observatory, which has
been in operation since 1999. But Chandra and IXPE aren’t quite looking at the same things.
Chandra is looking at the X-rays emitted by stellar-mass black holes among other things,
while IXPE wants to examine active galactic nuclei, quasars, pulsars, supernova remnants, and
more. By looking at the X-rays that these objects produce, we’re going to learn far more about them,
potentially even about the center of our own galaxy, which remains mysterious.
When it comes to the galactic center, we still have a lot to learn. We do know that there’s
a powerful radio source in the middle of the Milky Way, just like there is in the center of
every other galaxy. In 2020 scientists finally proved that this radio source is a black hole.
Called “Sagittarius A*”, it’s estimated to be around 4 million times more massive than the sun,
and there are some theories that there could be multiple black holes hiding there
rather than just the one. In recent years, other X-ray telescopes, specifically Chandra,
have made phenomenal discoveries about this region. The problem with studying the center is
that there’s so much gas and dust swirling around there that it completely obstructs our view.
Chandra, however, can cut through the white noise and map powerful X-ray sources that
would otherwise be totally hidden. IXPE is going to be able to do very similar things,
seeing through gas clouds to pinpoint large radio sources and massive objects.
It could finally show us exactly what’s lurking in the center of the galaxy. And if we can study
our own galactic center, this paves the way for studying other galactic centers we can observe.
Specifically, IXPE also wants to look at AGNs, or “active galactic nuclei”. An AGN is
an exceptionally bright and compact region in the center of a galaxy, something that the Milky Way,
which has an inactive galactic nucleus, lacks. The brightest AGNs of all are quasars, another
“dramatic” object that IXPE has its eyes on. A quasar is a supermassive black hole with a gaseous
accretion disc swirling around it. As this disc spirals down into the black hole, friction causes
it to heat up and it releases electromagnetic radiation. This energy is emitted in the form
of an “astrophysical jet”. A quasar with a jet pointing directly towards Earth is called a
blazar. IXPE specifically wants to see exactly how these jets are produced in quasars and blazars.
It's not just black holes that interest IXPE, either. Already, in early 2022,
IXPE has sent back an image of a supernova that happened hundreds of years ago. This
particular supernova remnant exploded in the 17th century and is called Cassiopeia A,
and with IXPE we can finally see the residue that it left behind.
The latest image of Cassiopeia mirrors one taken by Chandra in the 90s, but the new picture is
even more striking. The massive explosion of a supernova is certainly one of the most dramatic
and chaotic events to happen in the universe, and with every day that the IXPE mission continues,
we’re learning more and more about them – especially where x-rays are concerned.
But what about other, far stranger types of stars? Magnetars are magnetically powerful neutron stars,
themselves some of the brightest and densest objects in space, and IXPE wants to study
them as well. Because magnetars have a strong magnetic field they produce significantly more
X-rays than other astronomical objects, which is why IXPE is perfectly suited to study them.
Neutron stars alone are pretty weird and in need of further investigation, since they’re the dead
cores of giant stars that went supernova. They’re also denser than even white dwarf stars. But the
decay of the magnetic field of a magnetar is what produces these huge bursts of ionizing radiation,
all of which are totally invisible to the human eye and to non-specialized equipment. Magnetars
do all kinds of other strange things as well, including the emission of “fast radio bursts”,
another cosmic phenomenon we’re still studying. Similar to a magnetar is a “pulsar”, another
type of very magnetic neutron star. It’s unique because it creates huge beams of radiation, and
to us here on Earth, it seems like it’s pulsing. They’re actually not pulsing and are generally
continuously emitting these beams, but we can only see the beams when they’re coming towards us from
tens of thousands of lightyears away. Pulsars are so weird that when they were first discovered in
the late 1960s, some people believed that they were an alien radio source thanks to the power and
regularity of the signal. This “regularity” was just the rotation of the pulsar, and eventually,
we discovered so many that it became clear they’re not alien in origin at all. They really are just
bizarre neutron stars, and we still know very little about them. One thing NASA hopes that
IXPE will accomplish is discovering how, exactly, pulsars emit these concentrated bursts of x-ray
energy. The more we can learn about pulsars the better, because they could someday be used as
interstellar lighthouses – provided we ever come up with a way to travel between stars.
Pulsars also create something called “pulsar wind nebulae”. As we mentioned, neutron stars
are the leftover cores of massive stars that went supernova; a pulsar is a neutron star that emits
beams of electromagnetic radiation. A pulsar nebula emerges when the energy from a pulsar
charges the remnants of the supernova that formed it. The nebula spreads out far beyond the pulsar
and continually emits radiation from across the electromagnetic spectrum. These nebulae
don’t just produce X-rays, but also infrared rays and gamma-rays, becoming yet more potent energy
sources in the universe. We know very little about pulsar winds beyond this, though older studies
have tried to map the winds in 3D. Yet again, it was the Chandra X-Ray Observatory leading these
efforts, and the IXPE is going to continue them. One final mystery the IXPE could unravel
is that of X-ray binaries. These are binary star systems where the two stellar-mass objects
are innately intertwined. You could even describe it as a parasitic relationship.
There’s always a living star, but the other object could be another neutron star or a
black hole. They generate a lot of energy, often in the form of X-rays, because the black hole
pulls material from the star, creating a large accretion disk around itself much like the
disk that collects around a quasar. Some would even define these objects as “microquasars”.
There are so many complicated and powerful objects existing out there in our own galaxy and beyond,
and the Imaging X-Ray Polarimetry Explorer is just the latest attempt of many to understand them.
And that’s why NASA is studying the universe’s most dramatic objects.
What do you think? Is there anything we missed? Let us know in the comments, check out these other
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