M87

Sky at Night Magazine - - THE VIRGO GALAXIES -

Look at any im­age of the rich fields of gal­ax­ies in and around the con­stel­la­tion of Virgo, and among the stars and ga­lac­tic swirls that fill your view you’ll see nu­mer­ous bright ovals of light. These are el­lip­ti­cal gal­ax­ies and although they may not have the beauty or spec­tac­u­lar star-form­ing re­gions of their spi­ral cousins these of­ten vast stel­lar swarms are some of the most enig­matic in­ter­ga­lac­tic in­hab­i­tants we know of. Fore­most among the el­lip­ti­cals in this part of the sky is the gar­gan­tuan M87. It’s truly a gi­ant – a re­cent study by as­tronomers at the Euro­pean South­ern Ob­ser­va­tory was able to de­ter­mine the size of the halo of stars around the galaxy: the ring of stars spans about 980,000 lightyears, dwarf­ing the Milky Way’s stel­lar halo, which mea­sures roughly 640,000 lightyears across.

How­ever, M87’s most fa­mous fea­ture is not its size but what lies at its heart: a su­per­mas­sive black hole. Un­like the Milky Way’s cen­tral black hole M87’s is ac­tive. Im­ages of the galaxy show an enor­mous jet em­a­nat­ing from the black hole; the jet is glow­ing due to light re­leased by high-en­ergy par­ti­cles that are rac­ing at tremen­dous speeds along mag­netic field lines within it.

Aside from the jet and some glob­u­lar clus­ters, though, the rest of M87 might seem rather bland in vis­i­ble-light. At other wave­lengths, how­ever, a hid­den mael­strom of ac­tiv­ity in and around the enor­mous galaxy is re­vealed. Ra­dio tele­scopes, for ex­am­ple, have ob­served huge glow­ing streams of ma­te­rial as­so­ci­ated with the black-hole jet, while X-ray im­ages from the or­bit­ing Chan­dra ob­ser­va­tory show im­mense swirling clouds of su­per­heated gas within the galaxy. Some­thing to con­sider the next time you set eyes on that seem­ingly placid, fuzzy patch in your tele­scope’s eyepiece.

M87 is so vast that it pro­vides a home to sev­eral tril­lion stars and a su­per­mas­sive black hole; in­set: Chan­dra X-ray im­ages of M87 shows clouds of su­per­heated gas bil­low­ing in­side

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