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Today\u2019s NASA\/ESA Hubble Space Telescope\u00a0Picture of the Week\u00a0features a galaxy that\u2019s hard to categorise. The galaxy in question is NGC 2775, which lies 67 million light-years away in the constellation\u00a0Cancer\u00a0(The Crab). NGC 2775 sports a smooth, featureless centre that is devoid of gas, resembling an\u00a0elliptical galaxy. It also has a dusty ring with patchy star clusters, like a\u00a0spiral galaxy. Which is it, then: spiral or elliptical \u2014 or neither?<\/p>\n
Because we can only view NGC 2775 from one angle, it\u2019s difficult to say for sure. Some researchers have classified NGC 2775 as a spiral galaxy because of its feathery ring of\u00a0stars\u00a0and dust, while others have classified it as a lenticular galaxy. Lenticular galaxies have features common to both spiral and elliptical galaxies.<\/p>\n
It\u2019s not yet known exactly how lenticular galaxies come to be, and they might form in a variety of ways. Lenticular galaxies might be spiral galaxies that have merged with other galaxies, or that have mostly run out of star-forming gas and lost their prominent spiral arms. They also might have started out more similar to elliptical galaxies, then collected gas into a disk around them.<\/p>\n
Some evidence suggests that NGC 2775 has merged with other galaxies in the past. Invisible in this Hubble image, NGC 2775 has a tail of hydrogen gas that stretches almost 100\u00a0000 light-years around the galaxy. This faint tail could be the remnant of one or more galaxies that wandered too close to NGC 2775 before being stretched apart and absorbed. If NGC 2775 merged with other galaxies in the past, it could explain the galaxy\u2019s strange appearance today.<\/p>\n
A Hubble image of NGC 2775 was previously released in\u00a02020. The new version adds observations of a specific wavelength of red light that is emitted by clouds of hydrogen gas surrounding massive young stars.<\/p>\n
[Image Description:<\/i>\u00a0A galaxy seen face-on, with a slightly elliptical disc that appears to have a hole in the centre like a doughnut. In the hole, the core is a brightly glowing point that shines light out beyond the edge of the disc. Around the hole is an inner ring of dust, and at the galaxy\u2019s edge is a thicker outer ring of dust, with a swirling web of dust strands in between. Blue stars and red nebulae are visible behind the dust.]<\/p>\n<\/p><\/div>\n<\/p><\/div>\n