Light curve of OGLE-2017-BLG-1522. Credit: Jung et al., 2018.

Using microlensing technique, astronomers have found a new giant planet orbiting a brown dwarf located in the bulge of the Milky Way galaxy. The newly discovered exoplanet, designated OGLE-2017-BLG-1522Lb, is most likely 25 percent less massive than Jupiter. The finding is reported March 14 in a paper published on arXiv.org.

Based on the gravitational lens effect, the microlensing method is mainly used to detect planetary and stellar-mass objects regardless of the light they emit. This technique is therefore sensitive to the mass of the objects, especially to low-mass planets orbiting beyond the so-called "snow line" around relatively faint host stars like M dwarfs or brown dwarfs. Such planets are of special interest for astronomers, as just beyond this line, the most active planet formation occurs.

The OGLE-2017-BLG-1522 microlensing event was detected August 7, 2017 by the Optical Gravitational Lensing Experiment (OGLE) using the 1.3m Warsaw telescope at the Las Campanas Observatory in Chile. Afterward, an international team of astronomers, including scientists from the OGLE Collaboration and the Korea Microlensing Telescope Network (KMTNet) Collaboration, has analyzed the event and found a system composed of a brown dwarf orbited by a giant planet.

"We report the discovery of a giant planet in the OGLE-2017-BLG-1522 microlensing event. The planetary perturbations were clearly identified by high-cadence survey experiments despite the relatively short event timescale of t E ~ 7.5 days," the researchers wrote in the paper.

According to the study, OGLE-2017-BLG-1522Lb is a giant planet with a mass of about 0.75 Jupiter masses, orbiting its host at a distance of about 0.59 AU. The researchers noted that they are 75 percent sure that the host is a brown dwarf approximately 46 times more massive than our solar system's biggest planet. Therefore, additional observations should be conducted in order to definitely confirm whether the host is a low-mass star or a an intermediate-mass brown dwarf.

The projected companion-host separation indicates that OGLE-2017-BLG-1522Lb is placed beyond the snow line—the distance at which molecular species freeze, thus where the planet formation starts. Moreover, the authors of the paper calculated that the system is located in the galactic bulge.

In concluding remarks, the astronomers underlined the importance of their discovery, noting that OGLE-2017-BLG-1522Lb could be the first giant planet orbiting around a brown dwarf host having a planetary mass ratio.

"Planet formation scenarios combined with the small companion-host mass ratio q ∼ 0.016 and separation suggest that the companion could be the first discovery of a giant planet that formed in a protoplanetary disk around a brown dwarf host," the scientists concluded.

Explore further Extremely massive exoplanet discovered in the Milky Way's bulge

More information: OGLE-2017-BLG-1522: A giant planet around a brown dwarf located in the Galactic bulge, arXiv:1803.05095 [astro-ph.EP] OGLE-2017-BLG-1522: A giant planet around a brown dwarf located in the Galactic bulge, arXiv:1803.05095 [astro-ph.EP] arxiv.org/abs/1803.05095 Abstract

We report the discovery of a giant planet in the OGLE-2017-BLG-1522 microlensing event. The planetary perturbations were clearly identified by high-cadence survey experiments despite the relatively short event timescale of tE∼7.5 days. The Einstein radius is unusually small, θE=0.065mas, implying that the lens system either has very low mass or lies much closer to the microlensed source than the Sun, or both. A Bayesian analysis yields component masses (Mhost,Mplanet)=(46+79−25,0.75+1.26−0.40) MJ and source-lens distance DLS=0.99+0.91−0.54 kpc, implying that this is a brown-dwarf/Jupiter system that probably lies in the Galactic bulge, a location that is also consistent with the relatively low lens-source relative proper motion μ=3.2±0.5 mas yr−1. The projected companion-host separation is 0.59+0.12−0.11 AU, indicating that the planet is placed beyond the snow line of the host, i.e., asl∼0.12 AU. Planet formation scenarios combined with the small companion-host mass ratio q∼0.016 and separation suggest that the companion could be the first discovery of a giant planet that formed in a protoplanetary disk around a brown dwarf host.

© 2018 Phys.org</s>Scientists have discovered a planet a lot like Jupiter orbiting a dim star, if you can even call it a star—it’s nothing like our sun. The finding once again makes us wonder: what is a planet, anyway?

A team of researchers from two collaborations, KMTNet and the OGLE, or Optical Gravitational Lensing Experiment, announced their new planet-brown dwarf pair, calling it the “OGLE-2017-BLG-1522 microlensing event.” Brown dwarfs are either the lightest, dimmest stars or the heaviest, hottest planets. They have been spotted with companions before, but this would be largest mass difference between a brown dwarf and its companion yet, with the brown dwarf being perhaps over 60 times the size of the orbiting planet.

“OGLE-2017-BLG-1522Lb could be the first giant planet orbiting around a brown-dwarf host having a planetary mass ratio,” the authors write in the paper published on the arXiv preprint server.

That means that the planet could have formed from a ring of dust around the brown dwarf, rather than the two objects forming together as a sort of binary. “That’s the fundamental question,” Jennifer Yee, astrophysicist at the Harvard-Smithsonian Center for Astrophysics, told Gizmodo. “That’s why it’s important. We don’t know how you would form these things,” she said, referring to planets orbiting brown dwarfs.

The OGLE discovered the object on August 7, 2017, using their Warsaw telescope in Chile. Another network of telescopes in Chile, South Africa, and Korea, called the Korea Microlensing Telescope Network Survey, also monitored the event.

Essentially, the researchers saw another star, located behind the brown dwarf and planet, brighten in a characteristic pattern, one most likely due to the pair passing in front of it. The gravity from the closer objects would bend the light of the star behind them. The researchers attributed their results to a planet around three-quarters the mass of Jupiter orbiting a brown dwarf 46 or so times the mass of Jupiter. They calculated that the two are separated by about 0.6 times the distance between the Earth and the Sun.

This new paper hasn’t been published in its peer-reviewed form yet, and has some pretty large uncertainties; for example, the paper includes the line “the probability that the host is a brown dwarf is [approximately] 76%.” We’ll update this post with further comment when we hear back.



But the event brings up yet again the debate about what constitutes a “planet” and what doesn’t—a redefinition of the term planet stripped Pluto of its title, you might remember. It’s especially difficult to figure out the difference on the heavier end of things, though, when something is too big to be called a planet and just massive enough to become a star. How something forms is of crucial importance to understanding whether something is a planet or not, since planets tend to form from disks around stars, while stars form from the centers of the disks themselves.

Given the uncertainty, there’s still lots more research to be done, said Yee, since we can’t see the whole process from start to finish. “By finding a bunch of these thing, we can relate them back to the whole corse of their evolution,” she said.</s>According to Phys.org, Astronomers have made an interesting new discovery — a gas giant orbiting a brown dwarf. The exoplanet has been dubbed OGLE-2017-BLG-1522Lb. The newly discovered gaseous body has about 25% less mass than Jupiter, while its parent pseudo-star is about 46 times more massive than our own Jove.

Exoplanets are already pretty tough to spot. Unlike stars, planets don’t naturally give off any light, which means that scientists have to get a little creative when looking for them. Often they use something called the “Transit Method” wherein they follow a star as it crosses in front of its parents light, and watch how and where the image dims to get a rough estimate of its properties.

But this one was a bit different. Here, researchers used gravitational microlensing. Because gravity isn’t really a force, as Einstein demonstrated, but a curvature of space-time, in the same way a lens can be used to magnify an image, gravity can be used to accomplish the same. This technique requires solid understanding of the masses in the system being studied, but it’s extraordinarily effective and quite useful to spot a planet near a brown dwarf — which emit very little light naturally.

OGLE-2017-BLG-1522 was observed in August of last year as part of the Optical Gravitational Lensing Experiment (OGLE). The team used one of the telescopes at the Las Campanas Observatory in Chile, and, following the data collection, an international team of astronomers analyzed the data and found that the system likely had a brown dwarf and a gas giant.

“We report the discovery of a giant planet in the OGLE-2017-BLG-1522 microlensing event. The planetary perturbations were clearly identified by high-cadence survey experiments despite the relatively short event timescale of tE ~ 7.5 days,” the researchers wrote.

What matters here is that brown dwarfs aren’t generally thought to have the kind of nebulae that cause planet formation. There is a boundary, known as the “snow line,” past which planets tend to form. And while the astrophysics behind that gets a little complicated, these astronomers are fairly confident that their discovery is the first giant planet orbiting a brown dwarf with the right proportions. More observations will need to be made to confirm that the star is, indeed, brown, i.e. it doesn’t have enough mass to sustain hydrogen fusion in its core. If so, this could be a major new addition to our understanding of astrophysics and how planets form.

Let us know what you like about Geek by taking our survey.</s>Scientists have announced the first planet found to be orbiting a brown dwarf. It’s a significant discovery and a fascinating window into the evolution of a type of substellar object we don’t know much about.

A brown dwarf — sometimes referred to as a failed star — is an object of near-Jupiter size, but substantially greater mass. Unlike a normal star, it is not massive enough to fuse hydrogen and does not emit much visible light. Brown dwarfs can fuse deuterium and lithium, but never reached the size required to sustain hydrogen fusion in their cores.

As you might imagine, there are questions regarding when a super-planet (a planet of greater than Jupiter mass) gathers enough material to qualify as a brown dwarf. Because they aren’t particularly luminous, they aren’t all that easy to spot. The researchers in question note: “Our galaxy could also be teeming with brown dwarfs, which cannot sustain hydrogen fusion and thus are very faint.”

Now, here’s the catch: We’ve actually found very large planets orbiting brown dwarfs before. As the researchers note, however:

[The] large mass ratios (q & 0.1) between the host and the companion would suggest that they are formed as binary systems either by the dynamical interaction in unstable molecular clouds (Bate 2009, 2012) or by the turbulent fragmentation of molecular cloud cores (Padoan & Nordlund 2004). This implies that the companions could be considered as substellar objects rather than planets (Chabrier et al. 2014). By contrast, the low mass ratio of this event (q ∼ 0.016), combined with recent reports of the massive disks (& MJ) around young brown dwarfs (Hervey et al. 2012; Andr´e et al. 2012; Palau et al. 2014), suggest that the planetary companion of the event may be formed by planet formation mechanisms.

In other words: In the past, we’ve found planets that appear to have formed around brown dwarfs very differently than how we believe our sun and solar system were created. This planet appears to have been formed in the more normal fashion, suggesting that brown dwarf systems may be able to host planets (or at least a planet) as well.

The chances of such planets hosting life, however, are pretty slim. Brown dwarfs are not thought to be capable of emitting significant amounts of heat, since they contain relatively low amounts of fusable material in the first place. Old brown dwarfs are cool enough to have an atmosphere, though it isn’t one you want to breathe (it can rain iron in the atmosphere of a brown dwarf). Still, a brown dwarf with a planet around it is a surprising find and could tell us more about how planets form, even around exceptionally low-mass, not-quite-stars.
ArXiv publishes research that a gas giant may be orbiting a brown dwarf. The exoplanet, designated OGLE-2017-BLG-1522Lb, orbits its host at a distance of 0.59 AU and could be the first known gas giant to have formed inside the protoplanetary disk of a brown dwarf.