Nope, our Temporary Moon Isn’t Space Junk, it’s an Asteroid

In April of 2016, astronomers became aware of a distant object that appeared to be orbiting the Sun, but was also passing close enough to Earth that it could be periodically viewed using the most powerful telescopes. Since then, there has been ample speculation as to what this “Temporary Moon” could be, with most astronomers claiming that it is likely nothing more than an asteroid.

However, some suggested that it was a burnt-out rocket booster trapped in a near-Earth orbit. But thanks to new study by a team from the University of Arizona’s Lunar and Planetary Laboratory, this object – known as (469219) 2016 HO3 – has been confirmed as an asteroid. While this small near-Earth-asteroid orbits the Sun, it also orbits Earth as a sort of “quasi-satellite”.

The team that made this discovery was led by Vishnu Reddy, an assistant professor at the University of Arizona’s Lunar and Planetary Laboratory. Their research was also made possible thanks to NASA’s Near-Earth Object Observations Program. This program is maintained by NASA’s Center for Near-Earth Object Studies (CNEOS) and provides grants to institutions dedicated to the research of NEOs.

2016 HO3 is an asteroid that appears to orbit around Earth due to the mechanics of its peculiar orbit around the sun. Credit: NASA-JPL

The details of this discovery were presented this week at the 49th Annual Meeting of the Division for Planetary Sciences in Utah at a presentation titled “Ground-based Characterization of Earth Quasi Satellite (469219) 2016 HO3”. During the course of the presentation, Reddy and his colleagues described how they spotted the object using the Large Binocular Telescope (LBT) at the LBT Observatory on Mount Graham in southeastern Arizona.

According to their observations, 2016 HO3 measures just 100 meters (330 feet) across and is the most stable quasi-satellite discovered to date (of which there have been five). Over the course of a few centuries, this asteroid remains at a distance of 38 to 100 lunar distances – i.e. the distance between the Earth and the Moon. As Reddy explained in a UANews press statement, this makes the asteroid a challenging target:

“While HO3 is close to the Earth, its small size – possibly not larger than 100 feet – makes it challenging target to study. Our observations show that HO3 rotates once every 28 minutes and is made of materials similar to asteroids.”

Discovering the true nature of this object has also solved another big question – namely, where did 2016 HO3 come from? For those speculating that it might be space junk, it then became necessary to determine what the likely source of that junk was. Was it a remnant of an Apollo-era mission, or something else entirely? By determining that it is actually an NEO, Reddy and his team have indicted that it likely comes from the same place as other NEOs.

Vishnu Reddy of the University of Arizona’s Lunar Planetary Laboratory. Credit: Bob Demers/UANews

Reddy and his colleagues also indicated that 2016 HO3 reflected light off its surface in a way that is similar to meteorites that have been studied here on Earth. This was another indication that 2016 HO3 has similar origins to other NEOs (some of which have entered our atmosphere as meteors) which are generally asteroids that were kicked out of the Main Belt by Jupiter’s gravity.

“In an effort to constrain its rotation period and surface composition, we observed 2016 HO3 on April 14 and 18 with the Large Binocular Telescope and the Discovery Channel Telescope,” Reddy said. “The derived rotation period and the spectrum of emitted light are not uncommon among small NEOs, suggesting that 2016 HO3 is a natural object of similar provenance to other small NEOs.”

But unlike other NEOs which periodically cross Earth’s orbit, “quasi-satellites” are distinguished by their rather unique orbits. In the case of 2016 HO3, it has an orbit that follows a similar path to that the Earth’s; but because it is not dominated by the Earth’s gravity, their two orbits are out of sync. This causes 2016 HO3 to make annual loops around the Earth as it orbits the Sun.

Artist’s impression of a hypothetical astronaut mission to an asteroid. Credit: NASA Human Exploration Framework Team

Christian Veillet, one of co-authors of the presentation, is also the director of the LBT Observatory. As he explained, this characteristic could make “quasi-satellites” ideal targets for future NEO studies:

“Of the near-Earth objects we know of, these types of objects would be the easiest to reach, so they could potentially make suitable targets for exploration. With its binocular arrangement of two 8.4-meter mirrors, coupled with a very efficient pair of imagers and spectrographs like MODS, LBT is ideally suited to the characterization of these Earth’s companions.”

Similarly, their orbital characteristic could make “quasi-satellites” an ideal target for future space missions. One of NASA’s main goals in the coming decade is to send a crewed mission to a Near-Earth Object in order to test the Orion spacecraft and the Space Launch System. Such a mission would also help develop the necessary expertise for mounting missions deeper into space (i.e. to Mars and beyond).

The study of Near-Earth Objects is also of immense importance when it comes to determining how and where as asteroid might pose a threat to Earth. This knowledge allows for advanced warnings which can potentially save lives. It is also significant when it comes to the development of proposed counter-measures, several of which are currently being explored.

And be sure to enjoy this video of 2016 HO3’s orbit, courtesy of NASA’s Jet Propulsion Laboratory:

Further Reading: UANews

Star Should Have Gone Supernova, But it Imploded Into a Black Hole Instead

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 exploded 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.

Visible-light and near-infrared photos from NASA’s Hubble Space Telescope showing the giant star N6946-BH1 before and after it vanished out of sight by imploding to form a black hole. Credit: NASA/ESA/C. Kochanek (OSU)

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.

The details of their research appeared in a study titled “The Search for Failed Supernovae with the Large Binocular Telescope: Confirmation of a Disappearing Star“, which recently appeared in the Monthly Notices of the Royal Astronomical Society. Among the many galaxies they were watching for supernovas, they had their sights set on the Fireworks Galaxy to see what had become of N6946-BH1.

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 blackhole.

Simulated view of a black hole. Credit: Bronzwaer/Davelaar/Moscibrodzka/Falcke, Radboud University

As Scott Adams – a former Ohio State student who is now an astrophysicist at the Cahill Center for Astrophysics (and the lead author of the study) – explained in a NASA press release:

“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:

Further Reading: NASA, MNRAS

 

Have We Really Just Seen The Birth Of A Black Hole?

For almost half a century, scientists have subscribed to the theory that when a star comes to the end of its life-cycle, it will undergo a gravitational collapse. At this point, assuming enough mass is present, this collapse will trigger the formation of a black hole. Knowing when and how a black hole will form has long been something astronomers have sought out.

And why not? Being able to witness the formation of black hole would not only be an amazing event, it would also lead to a treasure trove of scientific discoveries. And according to a recent study by a team of researchers from Ohio State University in Columbus, we may have finally done just that.

The research team was led by Christopher Kochanek, a Professor of Astronomy and an Eminent Scholar at Ohio State. Using images taken by the Large Binocular Telescope (LBT) and Hubble Space Telescope (HST), he and his colleagues conducted a series of observations of a red supergiant star named N6946-BH1.

Artist’s impression of the star in its multi-million year long and previously unobservable phase as a large, red supergiant. Credit: CAASTRO / Mats Björklund (Magipics)
Artist’s impression of the star in its multi-million year long and previously unobservable phase as a large, red supergiant. Credit: CAASTRO / Mats Björklund (Magipics)

To break the formation process of black holes down, according to our current understanding of the life cycles of stars, a black hole forms after a very high-mass star experiences a supernova. This begins when the star has exhausted its supply of fuel and then undergoes a sudden loss of mass, where the outer shell of the star is shed, leaving behind a remnant neutron star.

This is then followed by electrons reattaching themselves to hydrogen ions that have been cast off, which causes a bright flareup to occur. When the hydrogen fusing stops, the stellar remnant begins to cool and fade; and eventually the rest of the material condenses to form a black hole.

However, in recent years, several astronomers have speculated that in some cases, stars will experience a failed supernova. In this scenario, a very high-mass star ends its life cycle by turning into a black hole without the usual massive burst of energy happening beforehand.

As the Ohio team noted in their study – titled “The search for failed supernovae with the Large Binocular Telescope: confirmation of a disappearing star” – this may be what happened to N6946-BH1, a red supergiant that has 25 times the mass of our Sun located 20 million light-years from Earth.

Artistic representation of the material around the supernova 1987A. Credit: ESO/L. Calçada
Artistic representation of the material around the supernova 1987A. Credit: ESO/L.

Using information obtained with the LBT, the team noted that N6946-BH1 showed some interesting changes in its luminosity between 2009 and 2015 – when two separates observations were made. In the 2009 images, N6946-BH1 appears as a bright, isolated star. This was consistent with archival data taken by the HST back in 2007.

However, data obtained by the LBT in 2015 showed that the star was no longer apparent in the visible wavelength, which was also confirmed by Hubble data from the same year. LBT data also  showed that for several months during 2009, the star experienced a brief but intense flare-up, where it became a million times brighter than our Sun, and then steadily faded away.

They also consulted data from the Palomar Transit Factory (PTF) survey for comparison, as well as observations made by Ron Arbour (a British amateur astronomer and supernova-hunter). In both cases, the observations showed evidence of a flare during a brief period in 2009 followed by a steady fade.

In the end, this information was all consistent with the failed supernovae-black hole model. As Prof. Kochanek, the lead author of the group’s paper – – told Universe Today via email:

“In the failed supernova/black hole formation picture of this event, the transient is driven by the failed supernova. The star we see before the event is a red supergiant — so you have a compact core (size of ~earth) out the hydrogen burning shell, and then a huge, puffy extended envelope of mostly hydrogen that might extend out to the scale of Jupiter’s orbit.  This envelope is very weakly bound to the star.  When the core of the star collapses, the gravitational mass drops by a few tenths of the mass of the sun because of the energy carried away by neutrinos.  This drop in the gravity of the star is enough to send a weak shock wave through the puffy envelope that sends it drifting away.  This produces a cool, low-luminosity (compared to a supernova, about a million times the luminosity of the sun) transient that lasts about a year and is powered by the energy of recombination.  All the atoms in the puffy envelope were ionized — electrons not bound to atoms — as the ejected envelope expands and cools, the electrons all become bound to the atoms again, which releases the energy to power the transient.  What we see in the data is consistent with this picture.”

The Large Binocular Telescope, showing the two imaging mirrors. Credit: NASA
The Large Binocular Telescope, showing the two imaging mirrors. Credit: NASA

Naturally, the team considered all available possibilities to explain the sudden “disappearance” of the star. This included the possibility that the star was shrouded in so much dust that its optical/UV light was being absorbed and re-emitted. But as they found, this did not accord with their observations.

“The gist is that no models using dust to hide the star really work, so it would seem that whatever is there now has to be much less luminous then that pre-existing star.” Kochanek explained. “Within the context of the failed supernova model, the residual light is consistent with the late time decay of emission from material accreting onto the newly formed black hole.”

Naturally, further observations will be needed before we can know whether or not this was the case. This would most likely involve IR and X-ray missions, such as the Spitzer Space Telescope and the Chandra X-ray Observatory, or one of he many next-generation space telescopes to be deployed in the coming years.

In addition, Kochanek and his colleagues hope to continue monitoring the possible black hole using the LBT, and by re-visiting the object with the HST in about a year from now. “If it is true, we should continue to see the object fade away with time,” he said.

The James Webb Space Telescope. Image Credit: NASA/JPL
Future missions, like the James Webb Space Telescope, will be able to observe possible failed supernovae/blackholes to confirm their existence. Credit: NASA/JPL

Needless to say, if true, this discovery would be an unprecedented event in the history of astronomy. And the news has certainly garnered its share of excitement from the scientific community. As Avi Loeb – a professor of astronomy at Harvard University – expressed to Universe Today via email:

“The announcement on the potential discovery of a star that collapsed to make a black hole is very interesting. If true, it will be the first direct view of the delivery room of a black hole. The picture is somewhat messy (like any delivery room), with uncertainties about the properties of the baby that was delivered. The way to confirm that a black hole was born is to detect X-rays. 

“We know that stellar-mass black holes exist, most recently thanks to the discovery of gravitational waves from their coalescence by the LIGO team. Almost eighty years ago Robert Oppenheimer and collaborators predicted that massive stars may collapse to black holes. Now we might have the first direct evidence that the process actually happens in nature.

But of course, we must remind ourselves that given its distance, what we could be witnessing with N6946-BH1 happened 20 million years ago. So from the perspective of this potential black hole, its formation is old news. But to us, it could be one of the most groundbreaking observations in the history of astronomy.

Much like space and time, significance is relative to the observer!

Further Reading: arXiv