A team of UNLV and International Astronomers Performed the First Large-sample, High-Resolution Survey of Protoplanetary Disks

Astronomers have classified almost 4,000 exoplanets in orbit around distant stars. Finding  these exoplanets has taught us many lessons but there is still much we don’t know about the birth of planets and the precise way they spawn the wide variety of planetary bodies we have already found, including so-called hot Jupiters, massive rocky worlds, icy dwarf planets, and -- hopefully someday soon -- distant analogs of Earth. 

To help answer these and other fascinating questions, a team of UNLV and international astronomers has performed the first large-sample, high-resolution survey of protoplanetary disks, the belts of dust and gas around young stars.

With the powerful Atacama Large Millimeter/submillimeter Array (ALMA) telescope, researchers have received stunning, high-resolution photos of 20 nearby protoplanetary disks that have provided astronomers with new insights into the variety of features they hold and the speed with which planets can emerge.

The results of this survey will be published in a special focus issue of the Astrophysical Journal Letters (ApJL).

Among the results: Shangjia Zhang, a first-year graduate student at UNLV  and Zhaohuan Zhu, am astrophysicist/professor led a study that used these ALMA features to find that in other parts of our Milky Way there is possibly a large population of young planets -- similar in mass to Neptune or Jupiter -- at wide-orbit that are not identifiable by other planet searching techniques we have today.

Zhu explained that this implies that many extrasolar systems may resemble our solar system in the sense that they also have Uranus and Neptune at the outer disk. In other words, our solar system could be a regular planetary system in our Milky Way.

Moreover, the UNLV researchers partnered with the international astronomy team on all nine other publications in this special ApJL focus issue.

For instance, understanding how Earth has formed 4 billion years ago in our solar system is tricky since our solar system finished the planet formation processes so long ago.

But, we can also observe young stars in other parts of the Milky Way where young stars and young planets are presently forming. But these young stars are far away from us, so we need powerful telescopes, such as ALMA, to examine these systems.

Zhu stated that "understanding planet formation helps us understand our origin.

Stars are surrounded by a flat disk made of gas and dust when they are young. These disks, known as protoplanetary disks, are where young planets are born (that is also why planets in our solar systems are coplanar, lying in a common plane around our sun).

Zhu also said that finding young planets embedded in this disk is like finding a pebble in a pond.

He explained that it is very difficult but, when they drop the pebble into the pond, it will cause ripples in the pond, which are more visible. Comparably, when young planets are present in its water pond (the protoplanetary disk), it will also cause waves. If the planet is large enough, these waves become a tsunami and result in damages to the disk, creating a gap along the planet's orbit in the disk.

ALMA can spot tiny ripples and gaps in protoplanetary disks. 

Zhang and Zhu performed a large set of numerical simulations to examine planet-disk interaction. Zhang evaluated 540 images from simulations to discover the correlation between the width of the gap and the planet mass and applied these relationships to observations to constrain the properties of potential planets in these disks.

Jessica Zeitz