A Galactic Traffic Jam

The barred spiral galaxy NGC 3887, seen here as viewed by the Wide Field Camera 3 aboard the NASA/ESA Hubble Space Telescope, lies over 60  million light-years away from us in the southern constellation of Crater (The Cup); it was discovered on 31 December 1785 by the German/British astronomer William Herschel.

Its orientation to us, while not exactly face-on, allows us to see NGC 3887’s spiral arms and central bulge in detail, making it an ideal target for studying a spiral galaxy’s winding arms and the stars within them. 

The very existence of spiral arms was for a long time a problem for astronomers. The arms emanate from a spinning core and should therefore become wound up ever more tightly, causing them to eventually disappear after a (cosmologically) short amount of time. It was only in the 1960s that astronomers came up with the solution to this winding problem; rather than behaving like rigid structures, spiral arms are in fact areas of greater density in a galaxy’s disc, with dynamics similar to those of a traffic jam. The density of cars moving through a traffic jam increases at the centre of the jam, where they move more slowly. Spiral arms function in a similar way; as gas and dust move through the density waves they become compressed and linger, before moving out of them again.

Credit:

ESA/Hubble & NASA, P. Erwin et al.

About the Image

Id:potw2009a
Type:Observation
Release date:2 March 2020, 06:00
Size:973 x 1009 px

About the Object

Name:NGC 3887
Type:Local Universe : Galaxy : Type : Spiral
Distance:60 million light years
Constellation:Crater
Category:Galaxies

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Coordinates

Position (RA):11 47 4.56
Position (Dec):-16° 51' 16.62"
Field of view:0.64 x 0.67 arcminutes
Orientation:North is 74.6° right of vertical

Colours & filters

BandWavelengthTelescope
Optical
g
475 nm Hubble Space Telescope
WFC3
Optical
I
814 nm Hubble Space Telescope
WFC3
Infrared
H
1.6 μm Hubble Space Telescope
WFC3

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