“Monster Planet” Discovered, Makes Scientists Rethink Theories of Planetary Formation

When it comes to how and where planetary systems form, astronomers thought they had a pretty good handle on things. The predominant theory, known as the Nebular Hypothesis, states that stars and planets form from massive clouds of dust and gas (i.e. nebulae). Once this cloud experiences gravitational collapse at the center, its remaining dust and gas forms a protoplanetary disk that eventually accretes to form planets.

However, when studying the distant star NGTS-1 – an M-type (red dwarf) located about 600 light-years away – an international team led by astronomers from the University of Warwick discovered a massive “hot Jupiter” that appeared far too large to be orbiting such a small star. The discovery of this “monster planet” has naturally challenged some previously-held notions about planetary formation.

The study, titled “NGTS-1b: A hot Jupiter transiting an M-dwarf“, recently appeared in the Monthly Notices of the Royal Astronomical Society. The team was led by Dr Daniel Bayliss and Professor Peter Wheatley from the University of Warwick and included members from the of the Geneva Observatory, the Cavendish Laboratory, the German Aerospace Center, the Leicester Institute of Space and Earth Observation, the TU Berlin Center for Astronomy and Astrophysics, and multiple universities and research institutes.

Artist’s impression of the cool red star above NGTS-1b. Credit: University of Warwick/Mark Garlick.

The discovery was made using data obtained by the ESO’s Next-Generation Transit Survey (NGTS) facility, which is located at the Paranal Observatory in Chile. This facility is run by an international consortium of astronomers who come from the Universities of Warwick, Leicester, Cambridge, Queen’s University Belfast, the Geneva Observatory, the German Aerospace Center, and the University of Chile.

Using a full array of fully-robotic compact telescopes, this photometric survey is one of several projects meant to compliment the Kepler Space Telescope. Like Kepler, it monitors distant stars for signs of sudden dips in brightness, which are an indication of a planet passing in front of (aka. “transiting”) the star, relative to the observer.  When examining data obtained from NGTS-1, the first star to be found by the survey, they made a surprising discovery.

Based on the signal produced by its exoplanet (NGTS-1b), they determined that it was a gas giant roughly the same size as Jupiter and almost as massive (0.812 Jupiter masses). Its orbital period of 2.6 days also indicated that it orbits very close to its star – about 0.0326 AU – which makes it a “hot Jupiter”. Based on these parameters, the team also estimated that NGTS-1b experiences temperatures of approximately 800 K (530°C; 986 °F).

The discovery threw the team for a loop, as it was believed to be impossible for planets of this size to form around small, M-type stars. In accordance with current theories about planet formation, red dwarf stars are believed to be able to form rocky planets – as evidenced by the many that have been discovered around red dwarfs of late – but are unable to gather enough material to create Jupiter-sized planets.

Artist’s concept of Jupiter-sized exoplanet that orbits relatively close to its star (aka. a “hot Jupiter”). Credit: NASA/JPL-Caltech)

As Dr. Daniel Bayliss, an astronomer with the University of Geneva and the lead-author on the paper, commented in University of Warwick press release:

“The discovery of NGTS-1b was a complete surprise to us – such massive planets were not thought to exist around such small stars. This is the first exoplanet we have found with our new NGTS facility and we are already challenging the received wisdom of how planets form. Our challenge is to now find out how common these types of planets are in the Galaxy, and with the new NGTS facility we are well-placed to do just that.”

What is also impressive is the fact that the astronomers noticed the transit at all. Compared to other classes of stars, M-type stars are the smallest, coolest and dimmest. In the past, rocky bodies have been detected around them by measuring shifts in their position relative to Earth (aka. the Radial Velocity Method). These shifts are caused by the gravitational tug of one or more planets that cause the planet to “wobble” back and forth.

In short, the low light of an M-type star has made monitoring them for dips in brightness (aka. the Transit Method) highly impractical. However, using the NGTS’s red-sensitive cameras, the team was able to monitored patches of the night sky for many months. Over time, they noticed dips coming from NGTS-1 every 2.6 days, which indicated that a planet with a short orbital period was periodically passing in front of it.

Artist’s impression of the planet orbiting a red dwarf star. Credit: ESO/M. Kornmesser

They then tracked the planet’s orbit around the star and combined the transit data with Radial Velocity measurements to determine its size, position and mass. As Professor Peter Wheatley (who leads NGTS) indicated, finding the planet was painstaking work. But in the end, its discovery could lead to the detection of many more gas giants around low-mass stars:

“NGTS-1b was difficult to find, despite being a monster of a planet, because its parent star is small and faint. Small stars are actually the most common in the universe, so it is possible that there are many of these giant planets waiting to found. Having worked for almost a decade to develop the NGTS telescope array, it is thrilling to see it picking out new and unexpected types of planets. I’m looking forward to seeing what other kinds of exciting new planets we can turn up.”

Within the known Universe, M-type stars are by far the most common, accounting for 75% of all stars in the Milky Way Galaxy alone. In the past, the discovery of rocky bodies around stars like Proxima Centauri, LHS 1140, GJ 625, and the seven rocky planets around TRAPPIST-1, led many in the astronomical community to conclude that red dwarf stars were the best place to look for Earth-like planets.

The discovery of a Hot Jupiter orbiting NGTS-1 is therefore seen as an indication that other red dwarf stars could have orbiting gas giants as well. Above all, this latest find once again demonstrates the importance of exoplanet research. With every find we make beyond our Solar System, the more we learn about the ways in which planets form and evolve.

Every discovery we make also advances our understanding of how likely we may be to discover life out there somewhere. For in the end, what greater scientific goal is there than determining whether or not we are alone in the Universe?

Further Reading: UofWarwick, RAS, MNRAS

Finally, An Explanation for the Alien Megastructure?

Back in October of 2015, astronomers shook the world when they reported how the Kepler mission had noticed a strange and sudden drop in brightness coming from KIC 8462852 (aka. Tabby’s Star). This was followed by additional studies that showed how the star appeared to be consistently dimming over time. All of this led to a flurry of speculation, with possibilities ranging from large asteroids and a debris disc to an alien megastructure.

But in what may be the greatest explanation yet, a team of researchers from Columbia University and the University of California, Berkley, have suggested that the star’s strange flickering could be the result of a planet it consumed at some point in the past. This would have resulted in a big outburst of brightness from which the star is now recovering; and the remains of this planet could be transiting in front of the star, thus causing periodic drops.

For the sake of their study – titled “Secular dimming of KIC 8462852 following its consumption of a planet“, which is scheduled to appear in the Monthly Notices of the Royal Astronomical Society – the team took the initial Kepler findings, which showed sudden drops of 15% and 22% in brightness. They then considered subsequent studies that took a look at the long-term behavior of Tabby’s Star (both of which were published in 2016).

Artist’s impression of an orbiting swarm of dusty comet fragments around Tabby’s Star. Could these be responsible for its peculiar dips in brightness or is there a biological reason?  A small red dwarf star (above, left) lies near Tabby’s. Credit: NASA/JPL-Caltech

The first study, conducted by Bradley Schaefer of Louisiana State University, showed a decrease of 14% between the years of 1890 and 1989. The second study, conducted by Ben Monet and Joshua Simon (of Caltech and the Carnegie Institution of Washington, respectively), showed how the star faded by 3% over the course of the four years that Kepler continuously viewed it.

They then attempted to explain this behavior using the Kozai Mechanism (aka. Kozai Effect, Lidov-Kozai mechanism), which is a long-standing method in astronomy for calculating the orbits of planets based on their eccentricity and inclination. Applied to KIC 8462852, they determined that the star likely consumed a planet (or planets) in the past, likely around 10,000 years ago.

This process would have caused a temporary brightening from which the star is now returning to normal (thus explaining the long term trend). They further determined that the periodic drops in brightness could be caused by the remnants of this planet passing in high-eccentricity orbits in front of the star, thus accounting for the sudden changes.

Their calculations also put mass constraints on the planet (or planets) consumed. By their estimates, it was either a single Jupiter-sized planet, or a large number of smaller objects – such as moon-mass bodies that were about 1 km in diameter. This latter possibility seems more inviting, since a large number of objects would have produced a field of debris that would be more consistent with the dimming rate observed by previous studies.

Artist’s concept of KIC 8462852, which has experienced unusual changes in luminosity over the past few years. Credit: NASA, JPL-Caltech

These results are not only the best explanation of this star’s strange behavior, they could have serious implications for the study of stellar evolution – in which stars gobble up some of their planets over time. As Brian D. Metzger, an assistant professor from the Columbia Astrophysics Laboratory and the lead author on the paper, explained in an interview with New Scientist:

“We estimated that if Tabby’s star were representative, something like 10 Jupiters would have to fall into a typical star over its lifetime, or maybe even more… These transits only last a few days, so when we see one, we have to alert all the telescopes and basically point every telescope we have at Tabby’s star.”

No doubt, the mystery of Tabby’s star will endure for some time to come. We can only hope that with ongoing observation, we might sort out exactly what is taking place in this far-flung system. But for the time being, the possibility that what are we seeing is the star returning to its normal state, and being occasionally dimmed by transiting pieces of debris, is the most plausible explanation yet.

Suffice it to say, the alien megastructure enthusiasts will likely be taking this latest study with a grain of salt! You have to admit, a megastructures is a VERY enticing possibility!

Further Reading: ArXiv

Supermassive Black Holes In Distant Galaxies Are Mysteriously Aligned

A supermassive black hole has been found in an unusual spot: an isolated region of space where only small, dim galaxies reside. Image credit: NASA/JPL-Caltech

In 1974, astronomers detected a massive source of radio wave emissions coming from the center of our galaxy. Within a few decades time, it was concluded that the radio wave source corresponded to a particularly large, spinning black hole. Known as Sagittarius A, this particular black hole is so large that only the designation “supermassive” would do. Since its discovery, astronomers have come to conclude that supermassive black holes (SMBHs) lie at the center of almost all of the known massive galaxies.

But thanks to a recent radio imaging by a team of researchers from the University of Cape Town and University of the Western Cape, in South Africa, it has been further determined that in a region of the distant universe, the SMBHs are all spinning out radio jets in the same direction. This finding, which shows an alignment of the jets of galaxies over a large volume of space, is the first of its kind, and could tell us much about the early Universe.

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