{"id":25028,"date":"2021-10-08T09:00:11","date_gmt":"2021-10-08T09:00:11","guid":{"rendered":"https:\/\/www.skyatnightmagazine.com\/?p=100606"},"modified":"2021-10-11T12:19:11","modified_gmt":"2021-10-11T12:19:11","slug":"how-to-locate-black-hole-cygnus-x-1","status":"publish","type":"rss_feed","link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/rss_feed\/how-to-locate-black-hole-cygnus-x-1\/","title":{"rendered":"How to locate black hole Cygnus X-1"},"content":{"rendered":"\n

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By Pete Lawrence\n \t\t<\/p>\n\n\n\n

Published: Friday, 08 October 2021 at 12:00 am<\/p>\n\n\n\n

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Cygnus X-1 is a source of X-rays in our Galaxy and the first such source to be attributed to the presence of a black hole.<\/p>\n

A black hole<\/a> is basically an object so massive that its escape velocity has exceeded the speed of light.<\/p>\n

As a consequence, no light can escape the object, leading to many strange space and time related phenomena.<\/p>\n

From an observational standpoint, Cygnus X-1 is essentially invisible to the naked eye.<\/p>\n

\""A\"<\/picture><\/div>\n
See if you can find HDE 226868, a star in a mutual orbit with a black hole. Credit: Pete Lawrence.<\/i><\/span><\/figcaption><\/span><\/i><\/div>\n

This isn\u2019t the end of the challenge though, for Cygnus X-1 is one component in a high mass X-ray binary system.<\/p>\n

The other component is a supergiant variable star<\/a> HDE 226868 (HIP 98298), which shines at mag. +9.0 and can be seen through a small telescope.<\/p>\n

The objects orbit one another, separated by just 0.2 AU. HDE 226868\u2019s stellar wind removes material from the star, which ends up spiralling around the black hole.<\/p>\n

The resulting accretion disc around the black hole is energetic and hot. This is the source of X-rays that gave away the existence of the HDE 226868\u2019s companion black hole.<\/p>\n

The challenge is to locate HDE 226868. The black hole can\u2019t be seen and this object\u2019s existence and nature will need to be provided by your imagination.<\/p>\n

\""An\"<\/picture><\/div>\n
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An image of the X-ray sources emitted by Cygnus X-1, as seen by the Chandra X-ray Observatory. Credit: NASA\/CXC<\/i><\/span><\/figcaption>\n

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The black hole is believed to have a mass equivalent to 21.2 solar masses contained within an effective radius of 44km.<\/p>\n

Locating a ninth magnitude star isn\u2019t in itself a complex task. However, it\u2019s located in Cygnus<\/a>, against the background of the Milky Way<\/a> and this will make it trickier.<\/p>\n

The key is to locate the mag. +3.9, naked-eye star Eta (\u03b7<\/span>) Cygni, which is located in the neck of the Swan between Sadr (Gamma (\u03b3<\/span>) Cygni) and Albireo (Beta (\u03b2<\/span>) Cygni).<\/p>\n

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The Cygnus and Lyra constellations. Credit: Bernhard Hubl \/ CCDGuide.com<\/i><\/span><\/figcaption>\n

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Look at the mid-point between these two easy naked-eye stars and offset slightly towards Sadr to identify Eta.<\/p>\n

HDE 226868 is located 25 arcminutes east and 6 arcminutes north of Eta Cygni. To star hop<\/a> to the target, centre up on Eta Cygni.<\/p>\n

Look 11 arcminutes to the east to find mag. +7.3 HIP 98193. Now head 18 arcminutes east of HIP 98193 <\/span>to get to mag. +8.9 TYC2678-2291-1, a star of similar brightness to HDE 226868.<\/span><\/p>\n

Drift <\/span>8 arcminutes to the north of TYC2678-2291-1 and a fraction west to locate HDE 226868 with a mag. +10 star an arcminute to its north.<\/p>\n

It may not look that special, but by observing HDE 226858 you\u2019re also looking at a black hole!<\/p>\n

Have you managed to observe HDE 226858? Let us know by emailing us at contactus@skyatnightmagazine.com<\/a>.<\/strong><\/em><\/p>\n

This guide originally appeared in the October 2021 issue of <\/strong><\/em>BBC Sky at Night Magazine<\/strong>.<\/strong><\/em><\/p>\n

<\/p><\/i><\/i><\/i>\n\n\n

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