Astronomers See a Newly Forming Planetary Disk That’s Continuing to Feed On Material from its Nebula

Over the last few years, astronomers have observed distant solar systems in their early stages of growth. ALMA (Atacama Large Millimeter/submillimeter Array) has captured images of young stars and their disks of material. And in those disks, they’ve spotted the tell-tale gaps that signal the presence of growing young planets.

As they ramped up their efforts, astronomers were eventually able to spot the young planets themselves. All those observations helped confirm our understanding of how young solar systems form.

But more recent research adds another level of detail to the nebular hypothesis, which guides our understanding of solar system formation.

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The Strange, Misshapen Orbits of Planet-Forming Disks in a Triple-Star System

Whatever we grow up with, we think of as normal. Our single solitary yellow star seems normal to us, with planets orbiting on the same, aligned ecliptic. But most stars aren’t alone; most are in binary relationships. And some are in triple-star systems.

And the planet-forming disks around those three-star systems can exhibit some misshapen orbits.

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Study Finds Bizarre Exoplanet Orbits for Binary Stars

Exoplanet surface

There’s an iconic scene in the original Star Wars movie where Luke Skywalker looks out over the desert landscape of Tatooine at the amazing spectacle of a double sunset. Now, a new study out of the National Radio Astronomy Observatory (NRAO) suggests that such exotic exoplanet worlds orbiting multiple stars may exist in misaligned orbits, far out of the primary orbital plane.

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Astronomers Finally Find the Neutron Star Leftover from Supernova 1987A

Astronomers at Cardiff University have done something nobody else has been able to do. A team, led by Dr. Phil Cigan from Cardiff University’s School of Physics and Astronomy, has found the neutron star remnant from the famous supernova SN 1987A. Their evidence ends a 30 year search for the object.

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Here’s a First. Astronomers See a Moon Forming Around a Baby Exoplanet

Astronomers have discovered, for the first time, moons forming in the disk of debris around a large exoplanet. Astronomers have suspected for a long time that this is how larger planets—like Jupiter in our own Solar System—get their moons. It’s all happening around a very young star named PDS 70, about 370 light years away in the constellation Centaurus.

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One of Our Best Views of the Supermassive Black Hole at the Heart of the Milky Way

Top left: simulation of Sgr A* at 86 GHz without interstellar scattering. Top right: simulation with interstellar scattering. Bottom right: observed image of Sgr A*. Bottom left: observed image of Sgr A* after removing the effects of interstellar scattering. Credit: S. Issaoun, M. Mo?cibrodzka, Radboud University/ M. D. Johnson, CfA

An almost unimaginably enormous black hole is situated at the heart of the Milky Way. It’s called a Supermassive Black Hole (SMBH), and astronomers think that almost all massive galaxies have one at their center. But of course, nobody’s ever seen one (sort of, more on that later): It’s all based on evidence other than direct observation.

The Milky Way’s SMBH is called Sagittarius A* (Sgr. A*) and it’s about 4 million times more massive than the Sun. Scientists know it’s there because we can observe the effect it has on matter that gets too close to it. Now, we have one of our best views yet of Sgr. A*, thanks to a team of scientists using a technique called interferometry.

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Bizarre Double Star System Flipped its Planetary Disk on its Side

Astronomers theorize that when our Sun was still young, it was surrounded by a disc of dust and gas from which the planets eventually formed. It is further theorized that the majority of stars in our Universe are initially surrounded in this way by a “protoplanetary disk“, and that in roughly 30% of cases, these disks will go on to become a planet or system of planets.

Ordinarily, these disks are thought to orbit around the equatorial band (aka. the ecliptic) of a star or system of stars. However, new research conducted by an international group of scientists has discovered the first example of a binary star system where the orientation was flipped and the disk now orbits the stars around their poles (perpendicular to the ecliptic).

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Here are 20 Protoplanetary Disks, With Newly Forming Planets Carving Out Gaps in the Gas and Dust

The hunt for other planets in our galaxy has heated up in the past few decades, with 3869 planets being detected in 2,886 systems and another 2,898 candidates awaiting confirmation. Though the discovery of these planets has taught scientists much about the kinds of planets that exist in our galaxy, there is still much we do not know about the process of planetary formation.

To answer these questions, an international team recently used the Atacama Large Millimeter/submillimeter Array (ALMA) to conduct the first large-scale, high-resolution survey of protoplanetary disks around nearby stars. Known as the Disk Substructures at High Angular Resolution Project (DSHARP), this program yielded high-resolution images of 20 nearby systems where dust and gas was in the process of forming new planets.

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Gas and Dust Seen Swirling Around our Galaxy’s Supermassive Black Hole

ALMA images show gas and dust swirling around the supermassive black hole at the center of the Milky Way. Image Credit: ALMA (ESO/NAOJ/NRAO)/ J. R. Goicoechea (Instituto de Física Fundamental, CSIC, Spain)

At the heart of the Milky Way Galaxy lurks a Supermassive Black Hole (SMBH) named Sagittarius A* (Sag. A-star). Sag. A* is an object of intense study, even though you can’t actually see it. But new images from the Atacama Large Millimetre/sub-millimetre Array (ALMA) reveal swirling high-speed clouds of gas and dust orbiting the black hole, the next best thing to seeing the hole itself.

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Simulated View of a Newly Forming Planetary System with Rings and Gaps

When searching for extra-solar planets, astronomers most often rely on a number of indirect techniques. Of these, the Transit Method (aka. Transit Photometry) and the Radial Velocity Method (aka. Doppler Spectroscopy) are the two most effective and reliable (especially when used in combination). Unfortunately, direct imaging is rare since it is very difficult to spot a faint exoplanet amidst the glare of its host star.

However, improvements in radio interferometers and near-infrared imaging has allowed astronomers to image protoplanetary discs and infer the orbits of exoplanets. Using this method, an international team of astronomers recently captured images of a newly-forming planetary system. By studying the gaps and ring-like structures of this system, the team was able to hypothesize the possible size of an exoplanet.

The study, titled “Rings and gaps in the disc around Elias 24 revealed by ALMA “, recently appeared in the Monthly Notices of the Royal Astronomical Society. The team was led by Giovanni Dipierro, an astrophysicist from the University of Leicester, and included members from the Harvard–Smithsonian Center for Astrophysics (CfA), the Joint ALMA Observatory, the National Radio Astronomy Observatory, the Max-Planck Institute for Astronomy, and multiple universities and research institutes.

Artist’s impression of circumstellar disc of debris around a distant star. Credit: NASA/JPL

In the past, rings of dust have been identified in many protoplanetary systems, and their origins and relation to planetary formation are the subject of much debate. On the one hand, they might be the result of dust piling up in certain regions, of gravitational instabilities, or even variations in the optical properties of the dust. Alternately, they could be the result of planets that have already developed, which cause the dust to dissipate as they pass through it.

As Dipierro and his colleagues explained in their study:

“The alternative scenario invokes discs that are dynamically active, in which planets have already formed or are in the act of formation. An embedded planet will excite density waves in the surrounding disc, that then deposit their angular momentum as they are dissipated. If the planet is massive enough, the exchange of angular momentum between the waves created by the planet and the disc results in the formation of a single or multiple gaps, whose morphological features are closely linked to the local disc conditions and the planet properties.”

For the sake of their study, the team used data from the Atacama Large Millimeter/sub-millimeter Array (ALMA) Cycle 2 observations – which began back in June of 2014. In so doing, they were able to image the dust around Elias 24 with a resolution of about 28 AU (i.e. 28 times the distance between the Earth and the Sun). What they found was evidence of gaps and rings that could be an indication of an orbiting planet.

From this, they constructed a model of the system that took into account the mass and location of this potential planet and how the distribution and density of dust would cause it to evolve. As they indicate in their study, their model reproduces the observations of the dust ring quite well, and predicted the presence of a Jupiter-like gas giant within forty-four thousand years:

“We find that the dust emission across the disc is consistent with the presence of an embedded planet with a mass of ?0.7?MJ at an orbital radius of ? 60?au… The surface brightness map of our disc model provides a reasonable match to the gap- and ring-like structures observed in Elias 24, with an average discrepancy of ?5?per?cent of the observed fluxes around the gap region.”

Thie sharpest image ever taken by ALMA showing the protoplanetary disc surrounding the young star HL Tauri. Credit: ALMA (ESO/NAOJ/NRAO)

 

These results reinforce the conclusion that the gaps and rings that have been observed in a wide variety of young circumstellar discs indicate the presence of orbiting planets. As the team indicated, this is consistent with other observations of protoplanetary discs, and could help shed light on the process of planetary formation.

“The picture that is emerging from the recent high resolution and high sensitivity observations of protoplanetary discs is that gap and ring-like features are prevalent in a large range of discs with different masses and ages,” they conclude. “New high resolution and high fidelity ALMA images of dust thermal and CO line emission and high quality scattering data will be helpful to find further evidences of the mechanisms behind their formation.”

One of the toughest challenges when it comes to studying the formation and evolution of planets is the fact that astronomers have been traditionally unable to see the processes in action. But thanks to improvements in instruments and the ability to study extra-solar star systems, astronomers have been able to see system’s at different points in the formation process.

This in turn is helping us refine our theories of how the Solar System came to be, and may one day allow us to predict exactly what kinds of systems can form in young star systems.

Further Reading: CfA, MNRAS