Cosmic search for a missing limb

This new Picture of the Week, taken by the NASA/ESA Hubble Space Telescope, shows the dwarf galaxy NGC 4625, located about 30 million light-years away in the constellation of Canes Venatici (The Hunting Dogs). The image, acquired with the Advanced Camera for Surveys (ACS), reveals the single spiral arm of the galaxy, which gives it an asymmetric appearance. But why is there only one spiral arm, when spiral galaxies normally have at least two?

Astronomers looked at NGC 4625 in different wavelengths in the hope of solving this cosmic mystery. Observations in the ultraviolet provided the first hint: in ultraviolet light the disc of the galaxy appears four times larger than on the image depicted here. An indication that there are a large number of very young and hot — hence mainly visible in the ultraviolet — stars forming in the outer regions of the galaxy. These young stars are only around one billion years old, about 10 times younger than the stars seen in the optical centre. At first astronomers assumed that this high star formation rate was being triggered by the interaction with another, nearby dwarf galaxy called NGC 4618.

They speculated that NGC 4618 may be the culprit “harassing” NGC 4625, causing it to lose all but one spiral arm. In 2004 astronomers found proof for this claim: The gas in the outermost regions of the dwarf galaxy NGC 4618 has been strongly affected by NGC 4625.

Credit:

ESA/Hubble & NASA

About the Image

Id:potw1746a
Type:Observation
Release date:13 November 2017, 06:00
Size:3386 x 1806 px

About the Object

Name:NGC 4625
Type:Local Universe : Galaxy : Component : Spiral Arm
Local Universe : Galaxy : Type : Spiral
Distance:30 million light years
Constellation:Canes Venatici
Category:Galaxies

Image Formats

Large JPEG
2.8 MB
Screensize JPEG
203.8 KB

Zoomable


Wallpapers

1024x768
408.6 KB
1280x1024
671.1 KB
1600x1200
954.1 KB
1920x1200
1.1 MB
2048x1536
1.5 MB

Coordinates

Position (RA):12 41 52.83
Position (Dec):41° 16' 25.90"
Field of view:2.82 x 1.50 arcminutes
Orientation:North is 22.5° left of vertical

Colours & filters

BandWavelengthTelescope
Optical
V
606 nm Hubble Space Telescope
ACS
Optical
V
555 nm Hubble Space Telescope
WFPC2
Optical
V
606 nm Hubble Space Telescope
ACS
Optical
I
814 nm Hubble Space Telescope
ACS
Optical
NII
658 nm Hubble Space Telescope
WFPC2
Optical
I
814 nm Hubble Space Telescope
ACS

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