Tardigrades are virtually microscopic critters that are extremophiles in the most, well, extreme sense. They often go by the name “water bears” (or sometimes “moss piglets”) because, while they are segmented and have eight legs, when magnified, they look like adorable, chubby little gummy bears — scientifically speaking.
Water bears prefer to live in moist environments like within the sediment at the bottom of lakes. But these hearty animals can survive unbelievable temperatures, radiation, extreme pressure, and so much more. This is why, according to a recent study published in Natureby researchers from the Oxford and Harvard, tardigrades might be the last species (of anything on Earth) still alive when the Sun dies.
The Last Species
David Sloan was part of the team that explored whether or not tardigrades could survive asteroid impact, gamma ray bursts, and supernovae (the explosion marking the death of a star). “To our surprise we found that although nearby supernovae or large asteroid impacts would be catastrophic for people, tardigrades could be unaffected,” Sloan said in an interview for a Harvard press release. “Therefore it seems that life, once it gets going, is hard to wipe out entirely.”
So, if these researchers are right, why does it matter? Well, this research helps to advance more than just the understanding of tardigrade biology. With the discovery of Trappist-1, recent obstacles found in the search for life on Mars, and the potential to find life on Titan, the study of extremophiles is essential to the quest to find life outside of Earth.
The better that we understand the limits and boundaries of life as we know it to exist on Earth, the better equipped we will be to search for life in the cosmos.
Supernovas are a celestial double-edged sword: they represent the violent death of a star and pose an immediate threat to anything within cosmic striking distance. But they also create a chemical cocktail capable of giving birth to new stars. That is, after all, the prevailing theory for the beginning of our Universe. What we know of supernovas, however, is limited by what the technology we have to observe them can tell us. Unless, of course, the eruptions are unfathomably massive — which is what happened 30 some years ago when a supernova 168,000 light-years away exploded with such intensity, and such magnitude, that it was visible with the naked eye. Supernova 1987A was the first event in more than 400 years that allowed astronomers to see — with their own two eyes — what a star exploding with the brightness of a 100 million suns looked like.
That was several decades ago, however, and technological advancement in the interim has given researchers today greater capabilities for analyzing Supernova 1987A. In Chile, the Atacama Large Millimetre/submillimetre Array (ALMA) has helped a group of researchers to create a 3D model of how that cosmic dust shapes into new stars. They also discovered several chemical elements, like silicon monoxide (SiO) and carbon monoxide (CO), which had never before been detected within the heart of the supernova. The researchers undertook a separate study to look for additional chemicals and found formyl cation (HCO+) and sulfur monoxide (SO) as well — which are findings that may even be more thrilling than the 3D modeling of a star’s birth. If these chemical formations have gone undetected, and we now have the means to reveal them, it begs the question: what other secrets may be lurking in a supernova’s core?
“This is the first time that we’ve found these species of molecules within supernovae,” said Mikako Matsuura, one of the researchers from Cardiff University, “which questions our long held assumptions that these explosions destroy all molecules and dust that are present within a star.”
Collapsing stars are a rare thing to witness. And when astronomers are able to catch a star in the final phase of its evolution, it is a veritable feast for the senses. Ordinarily, this process consists of a star undergoing gravitational collapse after it has exhausted all of its fuel, and shedding its outer layers in a massive explosion (aka. a supernova). However, sometimes, stars can form black holes without the preceding massive explosion.
This process, what might be described as “going out not with a bang, but with a whimper,” is what a team of astronomers witnessed when observing N6946-BH1 — a star located in the Fireworks Galaxy (NGC 6946). Originally, astronomers thought that this star would explode because of its significant mass. But instead, the star simply fizzled out, leaving behind a black hole.
The Fireworks Galaxy, a spiral galaxy located 22 million light-years from Earth, is so-named because supernova are known to be a frequent occurrence there. In fact, earlier this month, an amateur astronomer spotted what is now designated as SN 2017eaw. As such, three astronomers from Ohio Sate University (who are co-authors on the study) were expecting N6946-BH1 would go supernova when in 2009, it began to brighten.
However, by 2015, it appeared to have winked out. As such, the team went looking for the remnants of it with the help of colleagues from Ohio State University and the University of Oklahoma. Using the combined power of the Large Binocular Telescope (LBT) and NASA’s Hubble and Spitzer space telescopes, they realized that the star had completely disappeared from sight.
After it experienced a weak optical outburst in 2009, they had anticipated that this red supergiant would go supernova – which seemed logical given that it was 25 times as massive as our Sun. After winking out in 2015, they had expected to find that the star had merely dimmed, or that it had cast off a dusty shell of material that was obscuring its light from view.
Their efforts included an LBT survey for failed supernovae, which they combined with infrared spectra obtained by the Spitzer Space Telescope and optical data from Hubble. However, all the surveys turned up negative, which led them to only one possible conclusion: that N6946-BH1 must have failed to go supernova and instead went straight to forming a black hole.
N6946-BH1 is the only likely failed supernova that we found in the first seven years of our survey. During this period, six normal supernovae have occurred within the galaxies we’ve been monitoring, suggesting that 10 to 30 percent of massive stars die as failed supernovae. This is just the fraction that would explain the very problem that motivated us to start the survey, that is, that there are fewer observed supernovae than should be occurring if all massive stars die that way.
A major implication of this study is the way it could shed new light on the formation of very massive black holes. For some time now, astronomers have believed that in order to form a black hole at the end of its life cycle, a star would have to be massive enough to cause a supernova. But as the team observed, it doesn’t make sense that a star would blow off its outer layers and still have enough mass left over to form a massive black hole.
As Christopher Kochanek — a professor of astronomy at The Ohio State University, the Ohio Eminent Scholar in Observational Cosmology and a co-author of the team’s study — explained:
The typical view is that a star can form a black hole only after it goes supernova. If a star can fall short of a supernova and still make a black hole, that would help to explain why we don’t see supernovae from the most massive stars.
This information is also important as far as the study of gravitational waves goes. In February of 2016, scientists at the Laser Interferometer Gravitational-wave Observatory (LIGO) announced the first detection of this strange phenomena, which were apparently generated by a massive black hole. If in fact massive black holes form from failed supernova, it would help astronomers to track down the sources more easily.
Be sure to check out this video of the observations made of this failed SN and black hole:
While scientists have already uncovered answers to some of the universe’s greatest mysteries, there’s still a great deal we don’t understand — the “alien megastructure” star, fast radio bursts (FRBs), and the (non-)existence of dark matter are just a few examples. Thanks to new research by a team of astronomers, we may now be able to exclude from this list the previously unexplained mystery of antimatter in the Milky Way.
Essentially, antimatter is matter with its electrical charge reversed. For example, an electron’s antiparticle is a positron, while a proton’s antiparticle is an antiproton. When a particle of matter meets its antimatter cohort, they release a burst of energy and annihilate each other.
Some 40 years ago, scientists detected gamma rays that suggested that around 1043 positrons were being annihilated in the Milky Way every second. They believe most were concentrated in the central bulge of the galaxy, which didn’t make sense as that area hosts less than half of the galaxy’s total mass. As Roland Crocker, particle astrophysicist at the Australian National University, told Space.com, “The origin of these positrons is a 40-year-old mystery in astrophysics.”
That mystery may finally have a resolution, and it’s a relatively simple one.“You don’t need anything exotic like dark matter to explain the positrons,” claims Crocker. Instead, he and his research team suggest that the positrons may have come from just one kind of supernova. Their study has been published in Nature Astronomy.
Dead Stars, Lost Stars
Crocker’s team thinks that dim supernovas known as SN 1991bg-like could create all of those unexplained positrons. These supernovas result from the merging of two superdense white dwarf stars, and they generate a huge number of radioactive isotopes known as titanium-44, which is capable of releasing the positrons being annihilated.
But why were these positrons concentrated at the interior of the Milky Way? The researchers explained that SN 1991bg-like supernovas — unlike those resulting from the death of young, massive stars — likely occur in galactic neighborhoods with stars roughly 3 billion to 6 billion years old. Our galaxy’s central bulge happens to have a population of stars older than those in its outer disk.
Of course, while the simplest explanation does often prove to be the right one, Crocker isn’t ruling out a more exciting solution to this decades-old mystery. “The most recent data show that there’s a positron source connected to the very center of the galaxy,” he said. “In our model, this is explained as due to the old stars distributed on roughly 200-parsec [650 light years] scales around the galaxy’s supermassive black hole, but the black hole itself is an interesting alternative source.”