{"id":30426,"date":"2022-03-23T09:50:28","date_gmt":"2022-03-23T09:50:28","guid":{"rendered":"https:\/\/www.skyatnightmagazine.com\/?p=106337"},"modified":"2022-03-23T10:49:18","modified_gmt":"2022-03-23T10:49:18","slug":"astronomers-find-evidence-of-an-exoplanet-outside-our-galaxy","status":"publish","type":"rss_feed","link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/rss_feed\/astronomers-find-evidence-of-an-exoplanet-outside-our-galaxy\/","title":{"rendered":"Astronomers find evidence of an exoplanet outside our Galaxy"},"content":{"rendered":"

<\/p>

By Ezzy Pearson\n \t\t<\/p>

Published: Wednesday, 23 March 2022 at 12:00 am<\/p>

\n\n

When you look up at the stars in the night sky, consider this: on average, every star you see has at least one planet in orbit around it.<\/p>\n

There are a lot of stars visible to the naked eye alone, so consider how many planets there must be.<\/p>\n

Orbiting those bright stars in the night sky may be some of the strangest exoplanets<\/a> you can think of: scorching hot Jupiters<\/a> and super-Earths, but also rocky, terrestrial planets orbiting in the habitable zone around their star, capable of supporting life.<\/p>\n

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An artist\u2019s impression of a hot Jupiter; a gas giant similar to Jupiter but orbiting much closer to its host star.Credit: NASA\/Ames\/JPL-Caltech<\/span><\/figcaption><\/div>\n

Since the mid-1990s, when the first exoplanets<\/a> were discovered, there has been an explosion in exoplanet hunting, with numerous ground-based observatories and space telescopes dedicated to the search.<\/p>\n

Think of the Kepler space telescope<\/a> or the Transiting Exoplanet Survey Satellite<\/a>, or less well-known missions like the NEID telescope<\/a> or the Nancy Grace Roman Space Telescope<\/a>.<\/p>\n

Even the Hubble Space Telescope has been used to hunt exoplanets<\/a>, and the newly-launched James Webb Space Telescope will search for exoplanets<\/a>, too.<\/p>\n

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An artist\u2019s impression of the Kepler space telescope scouring the sky Credit: NASA<\/span><\/figcaption><\/div>\n

But so far, much of the hunting has been done within our Galaxy. So what about those exoplanets that lie beyond our Galaxy? Could we ever catch a glimpse of them?<\/p>\n

It turns out astronomers may already have caught a glimpse of the first ever exoplanet to be detected outside our Galaxy.<\/p>\n

It lies in the famous Whirlpool Galaxy<\/a>, M51, in the constellation Canes Venatici<\/a> and is about 28 million lightyears from Earth.<\/p>\n

Evidence of the first exoplanet outside our Galaxy is leading the way to an exciting new era of planet hunting.<\/p>\n

Dr Rosanne Di Stefano<\/a> is a senior astrophysicist at the Smithsonian Astrophysical Observatory at the Harvard-Smithsonian Center for Astrophysics.<\/p>\n

We spoke to Dr Di Stefano to find out more.<\/p>\n

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Dr Rosanne Di Stefano is a senior astrophysicist at the Smithsonian Astrophysical Observatory at the Harvard-Smithsonian Center for Astrophysics.<\/span><\/figcaption><\/div>\n

\u00a0<\/p>\n

How did you discover evidence of an exoplanet in the Whirlpool Galaxy?<\/b><\/h3>\n

There was data that had been taken over a 20-year period by the Chandra X-ray Observatory and the XMM-Newton Observatory, which is a European project.<\/p>\n

And these observatories both look regularly at galaxies<\/a> outside the Milky Way.\u00a0There are some galaxies, like M51, that have been observed many times over the years.<\/p>\n

We were looking for a dip in the X-ray emission, and what we realised is that the passage of a planet in front of an X-ray source would give a dip that would tell us that the planet was there. This is a pretty big signal.<\/p>\n

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Transit photometry reveals exoplanets by observing periodic dimming of the star\u2019s light.<\/span><\/figcaption><\/div>\n

Why did you focus on the Whirlpool Galaxy?<\/b><\/h3>\n

It really had to do with our collaborator, Ryan Urquhart, then a graduate student, now a postdoctoral fellow at Michigan State, who used M51 (also known as the Whirlpool Galaxy), M101, the Pinwheel Galaxy<\/a> and M104, the Sombrero Galaxy<\/a>.<\/p>\n

So that was the data that was ready for us.<\/p>\n

Each galaxy has several dozen bright sources, and each of these sources has been observed many times over this 20-year period.<\/p>\n

So when this was put together for M51, for example, there was about 10 days\u2019 worth of observation time for each of the dozens of sources in that galaxy.<\/p>\n

This was a wonderful resource for us to start with and that was our motivation. We would have started with other galaxies, and now, in fact, we have moved on to other galaxies.<\/p>\n

What do we know about the exoplanet outside our Galaxy?<\/b><\/h3>\n

We can tell its size is likely to be similar to Saturn<\/a> and we can also tell roughly how fast it is moving around this X-ray binary \u2013 about 17km\/s.\u00a0That tells us that it\u2019s in a wide orbit.<\/p>\n

That\u2019s probably about all the information we\u2019re going to know for now as it will be a very long time before there\u2019s another transit.<\/p>\n

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Artist\u2019s impression of the first exoplanet candidate detected outside our galaxy. Credit: NASA<\/span><\/figcaption><\/div>\n

How difficult is it to find exoplanets outside our Galaxy?<\/b><\/h3>\n

There are many methods that are used within the Milky Way to find exoplanets.<\/p>\n

For example, you can use transits at optical wavelengths by taking a regular star that is emitting optical light and looking for what is generally a very tiny dip as a planet passes in front.<\/p>\n

Or you can study the velocity of a star and see it go back and forth.<\/p>\n

These methods wouldn\u2019t be able to succeed right now in other galaxies because, if a target galaxy is, say, 1,000 times farther away, then you would get a million times less light.<\/p>\n

When you look at other galaxies in the optical and infrared<\/a> wavelengths, there are hundreds of billions of stars whose light is superposed.<\/p>\n

Even if you\u2019re looking at a very tiny portion of the galaxy, the light that you receive is a mixture of light from many different stars and that makes it difficult \u2013 or impossible at this point in time \u2013 to pull out the signal of a transit or another subtle signal.<\/p>\n

Our use of X-ray allowed this discovery, but it really depends entirely on how big the X-ray source is relative to the planet.<\/p>\n

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An image of the Whirlpool Galaxy with a box showing the location of the exoplanet candidate. Credit: X-ray: NASA\/CXC\/SAO\/R. DiStefano, et al.; Optical: NASA\/ESA\/STScI\/Grendler<\/span><\/figcaption><\/div>\n

How important is it to find exoplanets outside our Galaxy?<\/b><\/h3>\n

This is a whole new way of exoplanet hunting. We know of over 5,000 exoplanets in our own Galaxy that have been found using other methods.<\/p>\n

A planet\u2019s significance really depends on whether that planet or the planetary system has something very unique about it.<\/p>\n

But here, we have taken a new method that has never been used before.<\/p>\n

We\u2019ve shown that it can find planet transits even in other galaxies, and we found a planet in a kind of system that has never been studied for planets before, so I would say because it\u2019s new, it\u2019s definitely significant.<\/p>\n

This interview originally appeared in the April 2022 issue of <\/strong><\/em>BBC Sky at Night Magazine<\/strong>.<\/strong><\/em><\/p><\/body><\/html>\n

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