Scientists think that a well-known bright star in the southern skies is secretly a “unique object” that has remained “hidden in plain sight” until now, a discovery that may offer an unprecedented glimpse into the mysterious innards of stars, reports a new study. 

Gamma (γ) Columbae, a star located about 870 light years from Earth, has long been classified as a typical massive star. Now, scientists have upended this view by suggesting that γ Columbae is the “stripped pulsating core of a massive star”—meaning that its atmosphere has been torn away to expose the nuclear fusion factory at the star’s center—according to a study published on Monday in Nature Astronomy.

The discovery of γ Columbae’s secret identity was “serendipitous,” said Norbert Przybilla, head of the Institute for Astro- and Particle Physics at the University of Innsbruck and a co-author of the study, in a call with Motherboard. “We were simply analyzing a large bunch of stars. From first sight, you wouldn't expect the star to be something special, but then, from more detailed analysis, it immediately became clear that it's something that we haven't seen so far.” 

“It's always surprising what you'll find if you look closer and closer,” he added.

Przybilla and his colleagues pointed to telltale signatures in γ Columbae’s light spectrum that indicate chemical abundances consistent with a star that has lost its outer atmospheric envelope. The team speculated that this gassy veil was likely tugged off by an unseen companion star that is close to γ Columbae, or that has possibly merged with it in recent years. 

As a result, γ Columbae has shrunk from a “normal” star that was about 12 times the mass of the Sun to an buck-naked core that is about five times as massive as the Sun. Astronomers can occasionally glimpse details about the cores of extremely massive stars in their late stages, called Wolf-Rayet stars, or the cores of “subdwarf” stars similar in scale to the Sun, but γ Columbae is the first exposed core in this mass range that has been spotted before. That makes the star “a unique testbed for stellar (binary) evolution, so far hidden in plain sight,” according to the study. 

“Having a naked stellar core of such a mass is unique so far,” Przybilla said, who called it an “oddball.” 

“We have through the Wolf-Rayet stars ideas about how the cores of very massive stars look, and through the subdwarf stars we know the the cores of low-mass stars look, but in the middle, in between, so far, we don't have much evidence,” he said. “This is the first step.”

Przybilla and his colleagues suggest that γ Columbae is currently going through a transitory phase of disequilibrium that will be incredibly brief, probably lasting just 10,000 years. Prior to this stage, γ Columbae was a regular massive star that had run out of hydrogen fusion in its core, prompting its outer gassy layers to expand and encompass a companion star in a common atmospheric envelope. Instabilities from this interaction then triggered the ejection of the envelope, and possibly a merger between the two stars. 

What remains is the incredibly hot center of the star, which is likely burning through helium at this point. The star will eventually regain its equilibrium by becoming an extremely hot core that will fuse heavier elements together for another million years or two, before ending its life in a dramatic type of stellar explosion called a stripped core-collapse supernovae. After that, the star will enter a long afterlife as a type of extremely dense remnant called a neutron star.

It is “very unique” to “find an object in this phase, because it only lasts for a few thousand years, probably—long for us humans but in astronomical timescales, very very short,” Przybilla said. “It will always stay as a peculiar object.” 

For this reason, γ Columbae offers an unparalleled window into the core forces that power stars, with the potential to unlock answers to a host of questions in astrophysics. In particular, the object can provide insights about the evolution of binary star systems, which can have more complicated lives than single-star systems, such as our solar system. Przybilla and his colleagues suggest that asteroseismology, which is the study of oscillations inside stars, would be especially helpful in probing the structure of the star.

“If you analyze earthquakes, you can look, really, into Earth, and how it is built on the inside, and this has to be done with γ Columbae,” Przybilla said. “I think we will get a very, very good idea how such a core looks on the inside.” 

“This is probably the most interesting factor of all, in terms of scientific outcome, because all the cores are hidden in the other stars and here we have a naked one, a stripped one, and that will leave a very particular signal in its pulsations,” he concluded. “We have to follow up on that.” 

NASA’s InSight mission, which landed on Mars in 2018, has spent years gazing into the red planet’s interior by recording “marsquakes” that ripple through this alien world, providing an unprecedented view of its enigmatic subterranean layers. 

Now, just as InSight is entering its final weeks of life, it has delivered another milestone discovery: the first detection of seismic waves on the surface of another planet. In contrast to the mission’s previous recordings of so-called “body waves” that rocked Mars’ deep interior, the surface waves have exposed never-before-seen details about the upper crust of the planet, which could shed light on longstanding mysteries, according to a pair of studies published on Thursday in Science.

A team led by Liliya Posiolova, the orbital science operations lead at Malin Space Science Systems, used NASA’s Mars Reconnaissance Orbiter (MRO) to trace the origin of the surface waves to a large space rock that struck Mars on Christmas Eve of 2021, according to the first study. Another team led by Doyeon Kim, a geophysicist and senior research scientist at ETH Zurich’s Institute of Geophysics, describes how the waves “expand the current understanding of crustal structure on Mars beyond the crustal layering inferred beneath the InSight landing site,” in the second study.

“Since detecting / identifying surface waves on Mars and using surface-wave-driven information were a part of the mission goals of InSight, all of our seismologists in the team were very thrilled!” Kim said in an email to Motherboard.

“Previous to the detection of surface waves on Mars, our understanding of the Martian crust has been limited to what's underneath the InSight landing site because we were only using body waves that dive deep into the mantle,” he continued. “Because the velocity of surface waves depends on frequency, the measurement of surface wave dispersion allows us to understand how seismic velocities vary across different crustal depths averaged along its path traveling from the source to receiver. Therefore, our study provides the first glance of the crustal structure on Mars away from the lander.” 

InSight, which stands for Interior Exploration using Seismic Investigations, Geodesy and Heat Transport, has detected more than 1,300 marsquakes during its lifespan, including a monster magnitude-5 marsquake this past May that holds the record for the biggest extraterrestrial earthquake ever. Most of these tremors were produced by shifting faults inside the planet, but a few of them were sparked by meteorites slamming into its surface.

InSight detected surface waves from one of these impacts when it occurred on December 24, 2021. Posiolova and her colleagues were then able to use MRO to pinpoint the location of the enormous 500-foot-wide crater that the space rock left in the Amazonis Planitia region of Mars, which is located more than 2,100 miles from InSight. In addition, the team was also able to link a slightly smaller crater in the Tempe Terra region, a whopping 4,600 miles from InSight, to a marsquake that the lander detected on September 18, 2021. 

“Both impacts generated craters >130 meters in diameter, making them the largest fresh craters identified since the beginning of the MRO mission 16 years ago,” Posiolova’s team noted in their study. “The seismic events have identifiable surface waves, distinguishing them from other recorded and analyzed events on Mars and indicating shallow sources. Before these events, surface waves had not been unambiguously identified on any terrestrial planet other than Earth.”

“The success in observing the formation of impact craters on Mars using instruments on several missions opens up a more detailed understanding of impact dynamics, atmospheric physics, and the exploration of planetary interiors,” the researchers added.

With this unprecedented data in hand, Kim and his colleagues were able to measure the velocity of the surface waves as they swept across thousands of miles of Martian terrain. The results show that the crustal properties of Mars are relatively similar across wide distances, even though the northern and southern hemispheres of the planet are dramatically different. 

Whereas the Martian south is mostly a highland plateau speckled with craters, the north is composed of volcanic lowlands that may have hosted a massive ocean more than three billion years ago. The mystery of how this “dichotomy” on Mars emerged has puzzled scientists for more than a century. Some scientists have suggested that the regions may have different compositions or structures, but the new study seems to cast doubt on that hypothesis, deepening the mystery behind the dichotomy. 

“As a consequence of our analysis of surface waves, we now understand that the crust of Mars north of the equatorial dichotomy (the topographic variation on Mars that divides the southern highlands and northern lowlands) has a relatively uniform crustal structure with depth, with a high shear velocity of ~3.2 kilometers/second,” Kim explained. “Moreover, the speed of which surface waves travel along the north vs. south of the dichotomy was very similar; which allowed us to think about whether the overall composition of the crust would then be perhaps fairly similar at least for those crustal depths of ~5 to 30 kilometers.”

The team also discovered that InSight’s landing site in western part of Mars’ Elysium Planitia region is unexpectedly different from almost every other area traversed by the surface waves. For some reason, the lander sits on Martian crust that is denser than other parts of the red planet, raising new questions about how this particular region evolved. 

In addition to the new studies from Science, another team published a paper in Nature Astronomy on Thursday, also based on InSight’s data, that suggests that magma may still be bubbling deep under Mars’ surface. Led by Simon Stähler, a seismologist at ETH Zurich, the study offers a tantalizing glimpse of Mars’ present-day geologic activity, which has implications for understanding planetary evolution in general.

“Across the solar system, a pattern emerges, where the present-day tectonics of the larger terrestrial planets, Mars, Venus and the Earth, is dominated by internal dynamics instead of purely passive cooling and shrinking, as is found on the smaller Moon and Mercury,” Stähler and his colleagues concluded in the study.

Given how many discoveries InSight has made in its brief time on Mars, it’s bittersweet to acknowledge that the mission will not survive to see 2023. Dust has been accumulating on InSight’s solar panels for years, starving it of power, and the lander is expected to die sometime in December. However, the mission has secured its legacy as the first seismologist on another planet, and its observations of the red planet’s interior will continue to inform our understanding of Mars, and other worlds, for years to come. 

“It is sad to face the fact that the mission will eventually come to an end at some point,” Kim said. “However, we are only starting to learn how complicated the seismic data collected from Mars are compared to similar datasets collected on Earth or the Moon that we are far more comfortable with.”

“During almost three years, the InSight team has uncovered so much about the Martian interior structure, such as the crust-mantle boundary, mantle transition zone, the iron-rich liquid outer core, etc.,” he concluded. “I am very glad that the mission lasted this far and we still have a long way to go for understanding the interior structure and dynamics of Mars which still remain largely enigmatic to date.”

Scientists have discovered that a special type of “ghost particle” is likely forged by gargantuan black holes known as blazars, a finding that sheds light on some of the most tantalizing mysteries about our universe, such as the origin of particles called cosmic rays.

Cosmic rays are extremely energetic bits of atomic matter that shoot across space at near light speed, suggesting they hail from powerful objects that act as natural particle accelerators. One way to pinpoint sources of cosmic rays is to look for astrophysical neutrinos, another type of high-energy particle that is probably forged by the same intense mechanisms as cosmic rays. 

Neutrinos are sometimes called ghost particles because they are so lightweight that they barely react to matter, and pass effortlessly through our bodies and planets such as Earth. While this makes them extraordinarily difficult to capture, it also means that neutrinos usually travel in a straight line through space, allowing astronomers to sometimes trace them back to a particular region of the sky. Discovering the source of astrophysical neutrinos can, therefore, indirectly point to the natural space factories that spew out cosmic rays.

Now, scientists led by Sara Buson, an astronomer at the Julius Maximilian University of Würzburg have presented new evidence that blazars “are astrophysical neutrino factories and hence, extragalactic cosmic-ray accelerators,” according to a recent study published in the Astrophysical Journal Letters. 

Blazars have already been floated as a potential source of cosmic rays, but the new study is the first to show “a firm indirect detection of extragalactic cosmic-ray factories,” Buson and her colleagues said in the study. 

“Neutrinos are the most elusive particles in the universe, capable of traveling nearly unimpeded across it,” the researchers said. “Despite the vast amount of data collected, a long-standing and unsolved issue is still the association of high-energy neutrinos with the astrophysical sources that originate them.” 

“Among the candidate sources of neutrinos, there are blazars, a class of extragalactic sources powered by supermassive black holes that feed highly relativistic jets, pointed toward Earth,” they continued. “Previous studies appear controversial, with several efforts claiming a tentative link between high-energy neutrino events and individual blazars, and others putting into question such relation. In this work, we show that blazars are unambiguously associated with high-energy astrophysical neutrinos at an unprecedented level of confidence.”

Buson and her colleagues reached this conclusion after cross-referencing data from the IceCube Neutrino Observatory in Antarctica, which is the most sensitive neutrino detector on Earth, with BZCat, a catalog of more than 3,500 objects that are likely blazars. The team performed a statistical analysis to see if astrophysical neutrinos captured in “hotspots” at IceCube might point back to specific blazers in BZCat. 

The results revealed that 10 of the 19 IceCube hotspots in the southern sky are probably linked to blazars, suggesting that astrophysical neutrinos, and therefore cosmic rays, originate in these explosive environments. That’s not to say that all blazars produce these high-energy particles, or that high-energy neutrinos and cosmic rays only come from blazars. But the clear connection between the particles and at least one source is still a big step forward in terms of understanding the high-energy universe.   

“Cosmic rays are charged particles of energies up to 1020 [electronvolts], far higher than the most powerful human-attained particle accelerator, i.e., the Large Hadron Collider (LHC),” the researchers said in the study. “The nature and origin of these particles arriving from deep outer space remain elusive and represent a foremost challenge for the astroparticle and astrophysics fields.” 

Given that astrophysical neutrinos are “unique smoking-gun signatures of a cosmic-ray source,” the team added, it’s important to keep looking for these energetic ghost particles with next-generation neutrino detectors.