Featured Research

from universities, journals, and other organizations

Astronomers find 18 new planets: Discovery is the largest collection of confirmed planets around stars more massive than the sun

Date:
December 2, 2011
Source:
California Institute of Technology
Summary:
Discoveries of new planets just keep coming and coming. A team of astronomers has found 18 Jupiter-like planets in orbit around massive stars. The discoveries further constrain theories of planet formation.

The twin telescopes at Keck Observatory in Hawaii. The astronomers used Keck to discover 18 new Jupiter-like planets orbiting massive stars.
Credit: Rick Peterson/ W.M. Keck Observatory

Discoveries of new planets just keep coming and coming. Take, for instance, the 18 recently found by a team of astronomers led by scientists at the California Institute of Technology (Caltech).

"It's the largest single announcement of planets in orbit around stars more massive than the sun, aside from the discoveries made by the Kepler mission," says John Johnson, assistant professor of astronomy at Caltech and the first author on the team's paper, which was published in the December issue of The Astrophysical Journal Supplement Series. The Kepler mission is a space telescope that has so far identified more than 1,200 possible planets, though the majority of those have not yet been confirmed.

Using the Keck Observatory in Hawaii -- with follow-up observations using the McDonald and Fairborn Observatories in Texas and Arizona, respectively -- the researchers surveyed about 300 stars. They focused on those dubbed "retired" A-type stars that are more than one and a half times more massive than the sun. These stars are just past the main stage of their life -- hence, "retired" -- and are now puffing up into what's called a subgiant star.

To look for planets, the astronomers searched for stars of this type that wobble, which could be caused by the gravitational tug of an orbiting planet. By searching the wobbly stars' spectra for Doppler shifts -- the lengthening and contracting of wavelengths due to motion away from and toward the observer -- the team found 18 planets with masses similar to Jupiter's.

This new bounty marks a 50 percent increase in the number of known planets orbiting massive stars and, according to Johnson, provides an invaluable population of planetary systems for understanding how planets -- and our own solar system -- might form. The researchers say that the findings also lend further support to the theory that planets grow from seed particles that accumulate gas and dust in a disk surrounding a newborn star.

According to this theory, tiny particles start to clump together, eventually snowballing into a planet. If this is the true sequence of events, the characteristics of the resulting planetary system -- such as the number and size of the planets, or their orbital shapes -- will depend on the mass of the star. For instance, a more massive star would mean a bigger disk, which in turn would mean more material to produce a greater number of giant planets.

In another theory, planets form when large amounts of gas and dust in the disk spontaneously collapse into big, dense clumps that then become planets. But in this picture, it turns out that the mass of the star doesn't affect the kinds of planets that are produced.

So far, as the number of discovered planets has grown, astronomers are finding that stellar mass does seem to be important in determining the prevalence of giant planets. The newly discovered planets further support this pattern -- and are therefore consistent with the first theory, the one stating that planets are born from seed particles.

"It's nice to see all these converging lines of evidence pointing toward one class of formation mechanisms," Johnson says.

There's another interesting twist, he adds: "Not only do we find Jupiter-like planets more frequently around massive stars, but we find them in wider orbits." If you took a sample of 18 planets around sunlike stars, he explains, half of them would orbit close to their stars. But in the cases of the new planets, all are farther away, at least 0.7 astronomical units from their stars. (One astronomical unit, or AU, is the distance from Earth to the sun.)

In systems with sunlike stars, gas giants like Jupiter acquire close orbits when they migrate toward their stars. According to theories of planet formation, gas giants could only have formed far from their stars, where it's cold enough for their constituent gases and ices to exist. So for gas giants to orbit nearer to their stars, certain gravitational interactions have to take place to pull these planets in. Then, some other mechanism -- perhaps the star's magnetic field -- has to kick in to stop them from spiraling into a fiery death.

The question, Johnson says, is why this doesn't seem to happen with so-called hot Jupiters orbiting massive stars, and whether that dearth is due to nature or nurture. In the nature explanation, Jupiter-like planets that orbit massive stars just wouldn't ever migrate inward. In the nurture interpretation, the planets would move in, but there would be nothing to prevent them from plunging into their stars. Or perhaps the stars evolve and swell up, consuming their planets. Which is the case? According to Johnson, subgiants like the A stars they were looking at in this paper simply don't expand enough to gobble up hot Jupiters. So unless A stars have some unique characteristic that would prevent them from stopping migrating planets -- such as a lack of a magnetic field early in their lives -- it looks like the nature explanation is the more plausible one.

The new batch of planets have yet another interesting pattern: their orbits are mainly circular, while planets around sunlike stars span a wide range of circular to elliptical paths. Johnson says he's now trying to find an explanation.

For Johnson, these discoveries have been a long time coming. This latest find, for instance, comes from an astronomical survey that he started while a graduate student; because these planets have wide orbits, they can take a couple of years to make a single revolution, meaning that it can also take quite a few years before their stars' periodic wobbles become apparent to an observer. Now, the discoveries are finally coming in. "I liken it to a garden -- you plant the seeds and put a lot of work into it," he says. "Then, a decade in, your garden is big and flourishing. That's where I am right now. My garden is full of these big, bright, juicy tomatoes -- these Jupiter-sized planets."

The other authors on the The Astrophysical Journal Supplement Series paper, "Retired A stars and their companions VII. Eighteen new Jovian planets," include former Caltech undergraduate Christian Clanton, who graduated in 2010; Caltech postdoctoral scholar Justin Crepp; and nine others from the Institute for Astronomy at the University of Hawaii; the University of California, Berkeley; the Center of Excellence in Information Systems at Tennessee State University; the McDonald Observatory at the University of Texas, Austin; and the Pennsylvania State University. The research was supported by the National Science Foundation and NASA.


Story Source:

The above story is based on materials provided by California Institute of Technology. The original article was written by Marcus Woo. Note: Materials may be edited for content and length.


Journal Reference:

  1. John Asher Johnson, Christian Clanton, Andrew W. Howard, Brendan P. Bowler, Gregory W. Henry, Geoffrey W. Marcy, Justin R. Crepp, Michael Endl, William D. Cochran, Phillip J. MacQueen, Jason T. Wright, Howard Isaacson. Retired A Stars and Their Companions. VII. 18 New Jovian Planets. The Astrophysical Journal Supplement Series, 2011; 197 (2): 26 DOI: 10.1088/0067-0049/197/2/26

Cite This Page:

California Institute of Technology. "Astronomers find 18 new planets: Discovery is the largest collection of confirmed planets around stars more massive than the sun." ScienceDaily. ScienceDaily, 2 December 2011. <www.sciencedaily.com/releases/2011/12/111202155801.htm>.
California Institute of Technology. (2011, December 2). Astronomers find 18 new planets: Discovery is the largest collection of confirmed planets around stars more massive than the sun. ScienceDaily. Retrieved July 31, 2014 from www.sciencedaily.com/releases/2011/12/111202155801.htm
California Institute of Technology. "Astronomers find 18 new planets: Discovery is the largest collection of confirmed planets around stars more massive than the sun." ScienceDaily. www.sciencedaily.com/releases/2011/12/111202155801.htm (accessed July 31, 2014).

Share This




More Space & Time News

Thursday, July 31, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Supply Ship Takes Off for International Space Station

Supply Ship Takes Off for International Space Station

AFP (July 30, 2014) The European Space Agency's fifth Automated Transfer Vehicle (ATV-5) is takes off to the International Space Station on an Ariane 5 rocket from French Guiana. Duration: 00:34 Video provided by AFP
Powered by NewsLook.com
Raw: Rocket Launches Into Space With Cargo Ship

Raw: Rocket Launches Into Space With Cargo Ship

AP (July 30, 2014) Arianespace launched a rocket Tuesday from French Guiana carrying a robotic cargo ship to deliver provisions to the International Space Station. (July 30) Video provided by AP
Powered by NewsLook.com
In Virginia, the Rise of a New Space Coast

In Virginia, the Rise of a New Space Coast

AP (July 30, 2014) Every summer, tourists make the pilgrimage to Chincoteague Island, Va. to see wild ponies cross the Assateague Channel. But, it's the rockets sending to supplies to the International Space Station that are making this a year-round destination. (July 30) Video provided by AP
Powered by NewsLook.com
Russia Saves Gecko Sex Satellite, Media Has Some Fun With It

Russia Saves Gecko Sex Satellite, Media Has Some Fun With It

Newsy (July 27, 2014) The satellite is back under ground control after a tense few days, but with a gecko sex experiment on board, the media just couldn't help themselves. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

    Environment News

    Technology News



      Save/Print:
      Share:

      Free Subscriptions


      Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

      Get Social & Mobile


      Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

      Have Feedback?


      Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
      Mobile: iPhone Android Web
      Follow: Facebook Twitter Google+
      Subscribe: RSS Feeds Email Newsletters
      Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins