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A new study has returned to a popular Milky Way attraction, formed by a fast-spinning dead star core that scientists say is one of the most powerful electromagnetic generators in the galaxy. 

At the heart of this colorful nebula is a so-called pulsar, a type of neutron star that blasts streams of high-energy particles through space as it revolves like a lighthouse beacon. This thing is what remains of a massive star that suffered a supernova explosion. 

By adding radio data to NASA‘s Chandra X-ray Observatory image, astronomers can now see that some of the features don’t match up at different light wavelengths, suggesting scientists still don’t fully understand how the pulsar wind interacts with the leftover supernova debris.  

Researchers hope that by further probing the mysterious object, MSH 15-52, they can learn how this type of event creates high-energy particles, some of which may become cosmic rays that could eventually reach Earth. 

The Chandra observatory took an image of the nebula more than 15 years ago. Recently, scientists used the Australia Telescope Compact Array to make detailed radio maps of this region in space, then combined them with the X-ray data. The findings from that work are published in The Astrophysical Journal. 

At about 1,700 years old, MSH 15-52, sometimes called the “cosmic hand” or “hand of God” for its unusual shape, is one of the youngest-known nebulas formed by pulsar wind. Located about 17,000 light-years away in the constellation Circinus, it’s also quite large, dwarfing the famous Crab Nebula. The hand stretches about 150 light-years.

That’s hard to imagine, given that the pulsar itself — the thing responsible for this scene — is only about 12 miles wide. But, make no mistake, it’s fast and powerful. The pulsar spins seven times per second. For the millennials out there, that’s about as fast as a CD revolves in a Discman. And the pulsar’s magnetic field is about 30 million times stronger than the most powerful steady magnet ever built on Earth.

In the new composite image, gold represents hydrogen gas in visible light, red represents radio waves, and blue, orange, and yellow represent X-rays. The “fingers” look purple where radio and X-rays overlap.

Particles from the pulsar form a bubble of glowing gas. The system is also linked to the surrounding supernova debris, RCW 89, the remains of the massive star explosion that created the pulsar. The new radio data reveals threadlike filaments that could result from the collision of the pulsar’s wind with the supernova’s debris.

Some bright X-ray features, like the pulsar’s jet and fingerlike shapes, don’t show up in radio waves. This means the particles that produce them are a higher-energy source.

“Highly energetic particles are leaking out from a shock wave — similar to a supersonic plane’s sonic boom — near the pulsar,”  according to the Chandra X-ray Observatory, “and moving along magnetic field lines to create the fingers.” 

For the supernova remnant, the radio waves match up with bright knots seen in X-rays and visible light. But surprisingly, that radio glow extends much farther, leaving the researchers somewhat baffled.  

To get to the bottom of the mystery, scientists will likely need more detailed computer models.

Einstein’s equations of general relativity describe gravity and the motion of cosmic objects. But wind the clock back far enough and you’ll typically encounter a singularity-a state of infinite density and temperature-where the laws of physics collapse. Cosmologists simply cannot solve Einstein’s equations in such extreme environments-their normal simplifying assumptions no longer hold. And the same impasse applies to objects involving singularities or extreme gravity, such as black holes.

One issue might be what cosmologists take for granted. They normally assume that the universe is ‘isotropic’ and ‘homogeneous’-looking the same in every direction to every observer. This is a very good approximation for the universe we see around us, and one that makes it possible to easily solve Einstein’s equations in most cosmic scenarios. But is this a good approximation for the universe during the Big Bang?

“You can search around the lamppost, but you can’t go far beyond the lamppost, where it’s dark-you just can’t solve those equations,” explains Lim. “Numerical relativity allows you to explore regions away from the lamppost.”

Beyond the Lamppost

Numerical relativity was first suggested in the 1960s and 1970s to try to work out what kinds of gravitational waves (ripples in the fabric of spacetime) would be emitted if black holes collided and merged. This is an extreme scenario for which it is impossible to solve Einstein’s equations with paper and pen alone-sophisticated computer code and numerical approximations are required. Its development received renewed focus when the LIGO experiment was proposed in the 80s, although the problem was only solved in this way in 2005, raising hopes that the method could also be successfully applied to other puzzles.

“You can search around the lamppost, but you can’t go far beyond the lamppost, where it’s dark-you just can’t solve those equations. Numerical relativity allows you to explore regions away from the lamppost,” says Eugene Lim.

One longstanding puzzle that Lim is particularly excited about is cosmic inflation, a period of extremely rapid expansion in the early universe. Inflation was initially proposed to explain why the universe looks the way it does today, stretching out an initially small patch, so that the universe looks similar across a vast expanse. “If you don’t have inflation, a lot of things fall apart,” explains Lim. But while inflation helps explain the state of the universe today, nobody has been able to explain how or why the baby universe had this sudden short-lived growth spurt.

The trouble is, to probe this using Einstein’s equations, cosmologists have to assume that the universe was homogeneous and isotropic in the first place-something which inflation was meant to explain. If you instead assume it started out in another state, then “you don’t have the symmetry to write down your equations easily,” explains Lim.

But numerical relativity could help us get around this problem-allowing radically different starting conditions. It isn’t a simple puzzle to solve, though, as there’s an infinite number of ways spacetime could have been before inflation. Lim is therefore hoping to use numerical relativity to test the predictions coming from more fundamental theories that generate inflation, such as string theory.

Cosmic Strings, Colliding Universes

There are other exciting prospects, too. Physicists could use numerical relativity to try to work out what kind of gravitational waves could be generated by hypothetical objects called cosmic strings-long, thin “scars” in spacetime-potentially helping to confirm their existence. They might also be able to predict signatures, or “bruises,” on the sky from our universe colliding with neighboring universes (if they even exist), which could help us verify the multiverse theory.

Excitingly, numerical relativity could also help reveal whether there was a universe before the Big Bang. Perhaps the cosmos is cyclic and goes though “bounces” from old universes into new ones-experiencing repeated rebirths, Big Bangs and big crunches. That’s a very hard problem to solve analytically. “Bouncing universes are an excellent example, because they reach strong gravity where you can’t rely on your symmetries,” says Lim. “Several groups are already working on them-it used to be that nobody was.”

Numerical relativity simulations are so complex that they require supercomputers to run. As the technology of these machines improves, we might expect significant improvement in our understanding of the universe. Lim is hoping the team’s new paper, which outlines the methods and benefits of numerical relativity, can ultimately help get researchers across different areas up to speed.

“We hope to actually develop that overlap between cosmology and numerical relativity so that numerical relativists who are interested in using their techniques to explore cosmological problems can go ahead and do it,” Lim says, adding, “and cosmologists who are interested in solving some of the questions they cannot solve, can use numerical relativity.”