M51/Whirpool Galaxy
Credit X-ray: NASA/CXC/SAO/R. DiStefano, et al.;
Optical: NASA/ESA/STScI/Grendler;
Illustration: NASA/CXC/M.Weiss
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Tour: Chandra Sees Evidence for Possible Planet in Another Galaxy - More Animations
Tour: Chandra Sees Evidence for Possible Planet in Another Galaxy - More Animations
Astronomers have found evidence for a possible planet candidate in the M51 ("Whirlpool") galaxy, potentially representing what would be the first planet seen to transit a star outside of the Milky Way. As reported in our latest press release, researchers used NASA's Chandra X-ray Observatory to detect the dimming of X-rays from an "X-ray binary", a system where a Sun-like star is in orbit around a neutron star or black hole. The authors interpret this dimming as being a planet passing in front of the neutron star or black hole.
The left panel of this graphic shows M51 in X-rays from Chandra (purple and blue) and optical light from NASA's Hubble Space Telescope (red, green, and blue). A box marks the location of the possible planet candidate, an X-ray binary known as M51-ULS-1. An artist's illustration in the right panel depicts the X-ray binary and possible planet. Material from the companion star (white and blue in illustration) is pulled onto the neutron star or black hole, forming a disk around the dense object (illustrated as red and orange). The material near the dense object becomes superheated, causing it to glow in X-ray light (white). The planet is shown beginning to pass in front of this source of X-rays.
Looking for the dimming of a star's light as something passes in front of it is called the transit technique. For years, scientists have discovered exoplanets using transits with optical light telescopes, which detect the range of light humans can see with their eyes and more. This includes both ground-based telescopes and space-based ones like NASA's Kepler mission. These optical light transit detections require very high levels of sensitivity because the planet is much smaller than the star it passes in front of, and, therefore, only a tiny fraction of the light is blocked.
M51-ULS-1 Transit Only
Animation Credit: NASA/CXC/A.Jubett
The scenario of a transit in an X-ray binary is different. Because a potential planet is close in size to the X-ray source around the neutron star or black hole, a transiting planet passing along Earth's line of sight could temporarily block most or all of the X-rays. This makes it possible to spot transits at greater distances — including beyond the Milky Way — than current optical light studies using transits. A separate graphic shows how X-rays from M51-ULS-1 temporarily decrease to zero during the Chandra observations.
While this is a tantalizing study, the case of an exoplanet in M51 is not ironclad. One challenge is that the planet candidate's large orbit in M51-ULS-1 means it would not cross in front of its binary partner again for about 70 years, thwarting any attempts for a confirming observation for decades. There is also the possibility that the dimming of X-rays is due to a passing cloud of gas near the M51-ULS-1, though the researchers think the data strongly favor the planet explanation.
Illustration Credit: NASA/CXC/M. Weiss
The paper describing these results appears in the latest issue of Nature Astronomy and is available online. The authors are Rosanne DiStefano (CfA), Julia Berndtsson (Princeton), Ryan Urquhart (Michigan State University), Roberto Soria (University of the Chinese Science Academy), Vinay Kashap (CfA), Theron Carmichael (CfA), and Nia Imara (now at the University of California at Santa Cruz). NASA's Marshall Space Flight Center manages the Chandra program. The Smithsonian Astrophysical Observatory's Chandra X-ray Center controls science from Cambridge Massachusetts and flight operations from Burlington, Massachusetts.
Fast Facts for M51/Whirlpool Galaxy:
Scale: Image is about 6 arcmin (49,000 light years) across.
Category: Normal Galaxies & Starburst Galaxies
Constellation: Canes Venatici
Observation Date: 11 pointings between March 2000 and October 2012
Observation Time: 232 hours 10 minutes (9 days 16 hours 10 min)
Obs. ID: 353, 354, 1622, 3932, 13812-13816, 15496, 15553
Instrument: ACIS
Also Known As: NGC 5194, NGC 5195
References: DiStefano, R., et al., 2021, Nature Astronomy (Published); PDF Document
Color Code: X-ray: purple and blue; Optical: red, green, and blue
Distance Estimate: About 28 million light years
The paper describing these results appears in the latest issue of Nature Astronomy and is available online. The authors are Rosanne DiStefano (CfA), Julia Berndtsson (Princeton), Ryan Urquhart (Michigan State University), Roberto Soria (University of the Chinese Science Academy), Vinay Kashap (CfA), Theron Carmichael (CfA), and Nia Imara (now at the University of California at Santa Cruz). NASA's Marshall Space Flight Center manages the Chandra program. The Smithsonian Astrophysical Observatory's Chandra X-ray Center controls science from Cambridge Massachusetts and flight operations from Burlington, Massachusetts.
Fast Facts for M51/Whirlpool Galaxy:
Scale: Image is about 6 arcmin (49,000 light years) across.
Category: Normal Galaxies & Starburst Galaxies
Constellation: Canes Venatici
Observation Date: 11 pointings between March 2000 and October 2012
Observation Time: 232 hours 10 minutes (9 days 16 hours 10 min)
Obs. ID: 353, 354, 1622, 3932, 13812-13816, 15496, 15553
Instrument: ACIS
Also Known As: NGC 5194, NGC 5195
References: DiStefano, R., et al., 2021, Nature Astronomy (Published); PDF Document
Color Code: X-ray: purple and blue; Optical: red, green, and blue
Distance Estimate: About 28 million light years
Source: NASA's Chandra X-Ray Observatory
