Nature, Published online: 28 July 2021; doi:10.1038/s41586-021-03667-0

One of the key predictions of general relativity, the bending of light around massive, compact objects, is observed for a supermassive black hole in the galaxy I Zwicky 1.

Portal origin URL: Soon to Launch: NASA Rocket Carrying Solar X-Ray ScannerPortal origin nid: 472872Published: Wednesday, July 28, 2021 - 12:31Featured (stick to top of list): noPortal text teaser: The Marshall Grazing Incidence X-ray Spectrometer, or MaGIXS, mission is about to take flight. The launch window opens at the White Sands Missile Range in New Mexico on July 30.Portal image: Photo of engineer in lab with sounding rocket payload in background

Nature, Published online: 27 July 2021; doi:10.1038/d41586-021-02052-1

Researchers spy a dusty, moon-forming disk surrounding a planet beyond the Solar System.

The researchers, from the University of Cambridge and the Max Planck Institute for Extra-terrestrial Physics, have shown how exoplanets in binary star systems – such as the ‘Tatooine’ planets spotted by NASA’s Kepler Space Telescope – came into being without being destroyed in their chaotic birth environment.

They studied a type of binary system where the smaller companion star orbits the larger parent star approximately once every 100 years – our nearest neighbour, Alpha Centauri, is an example of such a system.

“A system like this would be the equivalent of a second Sun where Uranus is, which would have made our own solar system look very different,” said co-author Dr Roman Rafikov from Cambridge’s Department of Applied Mathematics and Theoretical Physics.

Rafikov and his co-author Dr Kedron Silsbee from the Max Planck Institute for Extra-terrestrial Physics found that for planets to form in these systems, the planetesimals – planetary building blocks which orbit around a young star – need to start off at least 10 kilometres in diameter, and the disc of dust and ice and gas surrounding the star within which the planets form needs to be relatively circular.

The research, which is published in Astronomy and Astrophysics, brings the study of planet formation in binaries to a new level of realism and explains how such planets, a number of which have been detected, could have formed.

Planet formation is believed to begin in a protoplanetary disc – made primarily of hydrogen, helium, and tiny particles of ices and dust – orbiting a young star. According to the current leading theory on how planets form, known as core accretion, the dust particles stick to each other, eventually forming larger and larger solid bodies. If the process stops early, the result can be a rocky Earth-like planet. If the planet grows bigger than Earth, then its gravity is sufficient to trap a large quantity of gas from the disc, leading to the formation of a gas giant like Jupiter.

“This theory makes sense for planetary systems formed around a single star, but planet formation in binary systems is more complicated, because the companion star acts like a giant eggbeater, dynamically exciting the protoplanetary disc,” said Rafikov.

“In a system with a single star the particles in the disc are moving at low velocities, so they easily stick together when they collide, allowing them to grow,” said Silsbee. “But because of the gravitational ‘eggbeater’ effect of the companion star in a binary system, the solid particles there collide with each other at much higher velocity. So, when they collide, they destroy each other.”

Many exoplanets have been spotted in binary systems, so the question is how they got there. Some astronomers have even suggested that perhaps these planets were floating in interstellar space and got sucked in by the gravity of a binary, for instance.

Rafikov and Silsbee carried out a series of simulations to help solve this mystery. They developed a detailed mathematical model of planetary growth in a binary that uses realistic physical inputs and accounts for processes that are often overlooked, such as the gravitational effect of the gas disc on the motion of planetesimals within it.

“The disc is known to directly affect planetesimals through gas drag, acting like a kind of wind,” said Silsbee. “A few years ago, we realised that in addition to the gas drag, the gravity of the disc itself dramatically alters dynamics of the planetesimals, in some cases allowing planets to form even despite the gravitational perturbations due to the stellar companion.”

“The model we’ve built pulls together this work, as well as other previous work, to test the planet formation theories,” said Rafikov.

Their model found that planets can form in binary systems such as Alpha Centauri, provided that the planetesimals start out at least 10 kilometres across in size, and that the protoplanetary disc itself is close to circular, without major irregularities. When these conditions are met, the planetesimals in certain parts of the disc end up moving slowly enough relative to each other that they stick together instead of destroying each other.

These findings lend support to a particular mechanism of planetesimal formation, called the streaming instability, being an integral part of the planet formation process. This instability is a collective effect, involving many solid particles in the presence of gas, that is capable of concentrating pebble-to-boulder sized dust grains to produce a few large planetesimals, which would survive most collisions.

The results of this work provide important insights for theories of planet formation around both binary and single stars, as well as for the hydrodynamic simulations of protoplanetary discs in binaries. In future, the model could also be used to explain the origin of the ‘Tatooine’ planets – exoplanets orbiting both components of a binary – about a dozen of which have been identified by NASA’s Kepler Space Telescope.

 

Reference:
Kedron Silsbee and Roman R. Rafikov. ‘Planet Formation in Stellar Binaries: Global Simulations of Planetesimal Growth.’ Astronomy and Astrophysics (2021). DOI:10.1051/0004-6361/20214113

Astronomers have developed the most realistic model to date of planet formation in binary star systems.

Planet formation in binary systems is more complicated, because the companion star acts like a giant eggbeater, dynamically exciting the protoplanetary discRoman RafikovESO/L. Calçada/N. RisingerArtist’s impression of the planet around Alpha Centauri B

The text in this work is licensed under a Creative Commons Attribution 4.0 International License. Images, including our videos, are Copyright ©University of Cambridge and licensors/contributors as identified.  All rights reserved. We make our image and video content available in a number of ways – as here, on our main website under its Terms and conditions, and on a range of channels including social media that permit your use and sharing of our content under their respective Terms.

YesLicense type: Attribution

A team of astronomers has released new observations of nearby galaxies that resemble colourful cosmic fireworks. The images, obtained with the European Southern Observatory’s Very Large Telescope (ESO’s VLT), show different components of the galaxies in distinct colours, allowing astronomers to pinpoint the locations of young stars and the gas they warm up around them. By combining these new observations with data from the Atacama Large Millimeter/submillimeter Array (ALMA), in which ESO is a partner, the team is helping shed new light on what triggers gas to form stars.

Using the Atacama Large Millimetre/submillimeter Array (ALMA), in which the European Southern Observatory (ESO) is a partner, astronomers have unambiguously detected the presence of a disc around a planet outside our Solar System for the first time. The observations will shed new light on how moons and planets form in young stellar systems.

Nature, Published online: 21 July 2021; doi:10.1038/d41586-021-01908-w

There’s good news, and there’s …

Nature, Published online: 21 July 2021; doi:10.1038/s41586-021-03636-7

Cloud-top thermal images obtained by the Akatsuki orbiter show that Venus has almost null mean meridional circulation at the cloud top, because poleward circulation on the dayside is offset by equatorward circulation on the nightside.

Nature, Published online: 22 July 2021; doi:10.1038/d41586-021-01985-x

The trailblazing collaboration that first imaged a black hole turns its sights on a nearby black-hole jet.

Nature, Published online: 23 July 2021; doi:10.1038/d41586-021-02024-5

Nearly half of researchers surveyed in the United Kingdom and elsewhere reported problems, with people from marginalized groups most likely to be mistreated.

Nature, Published online: 23 July 2021; doi:10.1038/d41586-021-02010-x

Some astronomers argue the flagship observatory — successor to the Hubble Space Telescope — will memorialize discrimination. Others are waiting for more evidence.

Portal origin URL: Chandra Catches Slingshot During CollisionPortal origin nid: 472505Published: Thursday, July 15, 2021 - 09:00Featured (stick to top of list): noPortal text teaser: When the titans of space — galaxy clusters — collide, extraordinary things can happen. A new study using NASA's Chandra X-ray Observatory examines the repercussions after two galaxy clusters clashed.Portal image: Galaxy cluster Abell 1775

Portal origin URL: Hubble Returns to Full Science Observations and Releases New ImagesPortal origin nid: 472617Published: Monday, July 19, 2021 - 16:12Featured (stick to top of list): noPortal text teaser: NASA’s Hubble Space Telescope is back in business, exploring the universe near and far.Portal image: These early snapshots demonstrate Hubble's return to full science operations, following correction of a computer anomaly aboard the spacecraft.

Portal origin URL: NASA’s Webb to Explore a Neighboring, Dusty Planetary SystemPortal origin nid: 472665Published: Wednesday, July 21, 2021 - 09:18Featured (stick to top of list): noPortal text teaser: Researchers will take stock of the dust in the debris disk surrounding the nearby star Beta Pictoris.Portal image: A debris disk, which includes comets, asteroids, rocks of various sizes, and plenty of dust, orbits the star Beta Pictoris, which is blocked at the center of this 2012 image by a coronagraph aboard the Hubble Space Telescope.

Portal origin URL: Artificial Intelligence Helps Improve NASA’s Eyes on the SunPortal origin nid: 472681Published: Friday, July 23, 2021 - 10:00Featured (stick to top of list): noPortal text teaser: A group of researchers is using artificial intelligence techniques to calibrate some of NASA’s images of the Sun, helping improve the data that scientists use for solar research.Portal image: Two lines of images of the Sun. The top line gets darker and harder to see, while the bottom row stays a consistent brightly visible image.

The meteor is believed to have landed in a forest after flashes of light were seen across Norway.

Nature, Published online: 16 July 2021; doi:10.1038/d41586-021-01954-4

Working with the United Nations, scientists hope to establish standards for satellite ‘megaconstellations’ and reduce disruption of astronomical observations.