NASA's Kepler, Swift Missions Harvest ‘Pumpkin’ Stars

  • Released Thursday, October 27, 2016
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Dive into the Kepler field and learn more about the origins of these rapidly spinning stars.

Credit: NASA's Goddard Space Flight Center

Music: "Electric Cosmos" from Killer Tracks

Watch this video on the NASA Goddard YouTube channel.

Complete transcript available.

Astronomers using observations from NASA's Kepler and Swift missions have discovered a group of rapidly spinning stars that produce X-rays at more than 100 times the peak levels ever seen from the sun. The stars, which spin so fast they've been squashed into pumpkin-like shapes, are thought to be the result of close binary systems where two sun-like stars merge.

The 18 stars rotate in just a few days, on average, compared to the sun's nearly one month rotation. Their rapid rotation greatly amplifies the same kind of activity we see on the sun, such as sunspots and solar flares, resulting in enhanced X-ray output.

The most extreme member of the group, a K-type orange giant dubbed KSw 71, is more than 10 times larger than the sun, rotates in just 5.5 days, and produces X-ray emission 4,000 times greater than the sun does at solar maximum.

These rare stars were found as part of an X-ray survey of the original Kepler field of view. From 2009 to 2013, Kepler measured the brightness of more than 150,000 stars in a single patch of the sky to detect the regular dimming from planets passing in front of their host stars. The mission was immensely successful and continues on as the K2 mission, studying other parts of the sky.

Because the original field has been studied so well by Kepler and other missions, it is now one of the best-known parts of the sky. Astronomers decided to observe portions of the field using the X-ray and ultraviolet/optical telescopes on Swift to find X-ray sources that Kepler may have observed in visible light. The Kepler-Swift Active Galaxies and Stars Survey (KSwAGS) found 93 sources, half of which are active galaxies, where a central black hole drives the emissions. The other half are various types of X-ray stars, including the 18 "pumpkin" stars.

Forty years ago, Ronald Webbink at the University of Illinois, Urbana-Champaign noted that close binary systems cannot survive once the fuel supply of one star dwindles and it starts to enlarge. The stars coalesce to form a single rapidly spinning star initially residing in a so-called "excretion" disk formed by gas thrown out during the merger. The disk dissipates over the next 100 million years, leaving behind a very active, rapidly spinning star.

The KSwAGS pumpkin stars are thought to have shed their disks recently, which means Kepler and Swift have caught them at the end of a very brief evolutionary phase.

This artist's concept illustrates how the most extreme "pumpkin star" found by Kepler and Swift compares with the sun. Both stars are shown to scale. KSw 71 is larger, cooler and redder than the sun and rotates four times faster. Rapid spin causes the star to flatten into a pumpkin shape, which results in brighter poles and a darker equator. Rapid rotation also drives increased levels of stellar activity such as starspots, flares and prominences, producing X-ray emission over 4,000 times more intense than the peak emission from the sun. KSw 71 is thought to have recently formed following the merger of two sun-like stars in a close binary system. Credit: NASA's Goddard Space Flight Center/Francis Reddy

This artist's concept illustrates how the most extreme "pumpkin star" found by Kepler and Swift compares with the sun. Both stars are shown to scale. KSw 71 is larger, cooler and redder than the sun and rotates four times faster. Rapid spin causes the star to flatten into a pumpkin shape, which results in brighter poles and a darker equator. Rapid rotation also drives increased levels of stellar activity such as starspots, flares and prominences, producing X-ray emission over 4,000 times more intense than the peak emission from the sun. KSw 71 is thought to have recently formed following the merger of two sun-like stars in a close binary system.

Credit: NASA's Goddard Space Flight Center/Francis Reddy

Unlabeled version of the above illustration.Credit: NASA's Goddard Space Flight Center/Francis Reddy

Unlabeled version of the above illustration.

Credit: NASA's Goddard Space Flight Center/Francis Reddy

The designations and locations of 18 new "pumpkin" stars are shown on part of the first-light image of the original Kepler field. Using the X-ray and ultraviolet/optical telescopes aboard Swift, researchers studied four parts of the field for the Kepler-Swift Active Galaxies and Stars Survey (KSwAGS). KSwAGS imaged about six square degrees, or 12 times the apparent size of a full moon. The data revealed 18 rapidly rotating stars with X-ray emissions greater than 100 times the sun's at solar maximum. KSw 71 is located in the second field from lthe left.Credit: NASA Goddard/Francis Reddy and NASA Ames/J. Jenkins

The designations and locations of 18 new "pumpkin" stars are shown on part of the first-light image of the original Kepler field. Using the X-ray and ultraviolet/optical telescopes aboard Swift, researchers studied four parts of the field for the Kepler-Swift Active Galaxies and Stars Survey (KSwAGS). KSwAGS imaged about six square degrees, or 12 times the apparent size of a full moon. The data revealed 18 rapidly rotating stars with X-ray emissions greater than 100 times the sun's at solar maximum. KSw 71 is located in the second field from lthe left.

Credit: NASA Goddard/Francis Reddy and NASA Ames/J. Jenkins

A version of the above image without text. The locations of 18 new "pumpkin" stars are shown on part of the first-light image of the original Kepler field. Using the X-ray and ultraviolet/optical telescopes aboard Swift, researchers studied four parts of the field for the Kepler-Swift Active Galaxies and Stars Survey (KSwAGS). KSwAGS imaged about six square degrees, or 12 times the apparent size of a full moon. The data revealed 18 rapidly rotating stars with X-ray emissions greater than 100 times the sun's at solar maximum.Credit: NASA Goddard/Francis Reddy and NASA Ames/J. Jenkins

A version of the above image without text. The locations of 18 new "pumpkin" stars are shown on part of the first-light image of the original Kepler field. Using the X-ray and ultraviolet/optical telescopes aboard Swift, researchers studied four parts of the field for the Kepler-Swift Active Galaxies and Stars Survey (KSwAGS). KSwAGS imaged about six square degrees, or 12 times the apparent size of a full moon. The data revealed 18 rapidly rotating stars with X-ray emissions greater than 100 times the sun's at solar maximum.

Credit: NASA Goddard/Francis Reddy and NASA Ames/J. Jenkins

A version of the above images without annotations. Credit: NASA Ames/J. Jenkins

A version of the above images without annotations. Credit: NASA Ames/J. Jenkins

This is a modified version of the Kepler mission's first-light field of view. The original red coloring has been altered to better match the wider view of the summer sky included below. More information on the image is availabe here.Credit: NASA Ames/J. Jenkins

This is a modified version of the Kepler mission's first-light field of view. The original red coloring has been altered to better match the wider view of the summer sky included below. More information on the image is availabe here.

Credit: NASA Ames/J. Jenkins

This image highlights the KSwAGS fields studied by Swift in an outline of the orignal Kepler field superimposed on the starry sky. The outline shows the positions of paired CCD modules on the Kepler focal plane. The field occupies about 100 square degrees comprising parts of the constellations Cygnus and Lyra. Deneb, the brightest star in Cygnus, can be seen at left near the reddish glow of the North America Nebula. Vega, the brightest star in Lyra, lies below and to the right of the Kepler field.Credit: NASA Goddard Space Flight Center and Axel Mellinger, Central Michigan University

This image highlights the KSwAGS fields studied by Swift in an outline of the orignal Kepler field superimposed on the starry sky. The outline shows the positions of paired CCD modules on the Kepler focal plane. The field occupies about 100 square degrees comprising parts of the constellations Cygnus and Lyra. Deneb, the brightest star in Cygnus, can be seen at left near the reddish glow of the North America Nebula. Vega, the brightest star in Lyra, lies below and to the right of the Kepler field.

Credit: NASA Goddard Space Flight Center and Axel Mellinger, Central Michigan University

This image shows an outline of the orignal Kepler field of view superimposed on the starry sky. The outline shows the positions of paired CCD modules on the Kepler focal plane. The field occupies about 100 square degrees comprising parts of the constellations Cygnus and Lyra. Deneb, the brightest star in Cygnus, can be seen at left near the reddish glow of the North America Nebula. Vega, the brightest star in Lyra, lies below and to the right of the Kepler field.Credit: NASA Goddard Space Flight Center and Axel Mellinger, Central Michigan University

This image shows an outline of the orignal Kepler field of view superimposed on the starry sky. The outline shows the positions of paired CCD modules on the Kepler focal plane. The field occupies about 100 square degrees comprising parts of the constellations Cygnus and Lyra. Deneb, the brightest star in Cygnus, can be seen at left near the reddish glow of the North America Nebula. Vega, the brightest star in Lyra, lies below and to the right of the Kepler field.

Credit: NASA Goddard Space Flight Center and Axel Mellinger, Central Michigan University

A wide-field image of the starry sky including the constellations Cygnus and Lyra. Deneb, the brightest star in Cygnus, can be seen at left near the reddish glow of the North America Nebula. Vega, the brightest star in Lyra, lies below and to the right of center. Credit: Axel Mellinger, Central Michigan University

A wide-field image of the starry sky including the constellations Cygnus and Lyra. Deneb, the brightest star in Cygnus, can be seen at left near the reddish glow of the North America Nebula. Vega, the brightest star in Lyra, lies below and to the right of center.

Credit: Axel Mellinger, Central Michigan University

Illustration of two sun-like stars born together in a close binary system, thought to be the first step toward forming a star like KSw 71. Credit: NASA's Goddard Space Flight Center

Illustration of two sun-like stars born together in a close binary system, thought to be the first step toward forming a star like KSw 71.

Credit: NASA's Goddard Space Flight Center

In this artist's concept, the more massive star in a close binary system has begun to deplete its core fuel supply. The star has enlarged in response and now physically contacts its companion. This stars will merge together. Credit: NASA's Goddard Space Flight Center

In this artist's concept, the more massive star in a close binary system has begun to deplete its core fuel supply. The star has enlarged in response and now physically contacts its companion. This stars will merge together.

Credit: NASA's Goddard Space Flight Center

In this illustration, the merging process is nearly complete. Gas ejected from the equatorial region of the combined star forms an excretion disk around it. The disk dissipates over the next 100 million years, leaving behind a very active, rapidly spinning solitary star.Credit: NASA's Goddard Space Flight Center

In this illustration, the merging process is nearly complete. Gas ejected from the equatorial region of the combined star forms an excretion disk around it. The disk dissipates over the next 100 million years, leaving behind a very active, rapidly spinning solitary star.

Credit: NASA's Goddard Space Flight Center

Artist's concept animation of a star similar to KSw 71, where the excretion disk has fully dissipated.

Credit: NASA's Goddard Space Flight Center

For More Information

See http://www.nasa.gov/feature/goddard/2016/nasa-missions-harvest-a-passel-of-pumpkin-stars

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Please give credit for this item to:
NASA's Goddard Space Flight Center. Individual images should be credited as indicated above.

This page was originally published on Thursday, October 27, 2016.
This page was last updated on Wednesday, May 3, 2023 at 1:48 PM EDT.

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