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Cosmic Challenge: WLM and WLM-1

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Cosmic Challenge: WLM and WLM-1


December 2022

Phil Harrington

This month's suggested aperture range:

10-inch (25-cm) and larger telescopes












00m 01.9m

-15° 27.8'





Globular cluster

01m 04.8m

+02° 17.1'





If you thought last month's challenge, IC 1613, was just too easy, try your luck with another member of the Local Group that is also within Cetus.


Above: Early evening star map showing the location of this month's Cosmic Challenge.


Credit: Map adapted from Star Watch by Phil Harrington


Above: Finder chart for this month's Cosmic Challenge.


Credit: Chart adapted from Cosmic Challenge by Phil Harrington
Click on the chart to open a printable PDF version in a new window



The Wolf-Lundmark-Melotte Dwarf, or WLM for short, was discovered by Max Wolf three years after IC 1613. The true extragalactic nature of this dwarf irregular system remained unconfirmed, however, until 1926, when it was studied by Knut Lundmark and Philibert Melotte. Melotte published the results in a paper entitled New Nebulae shown on Franklin-Adams Chart Plates (Monthly Notices of the Royal Astronomical Society, Vol. 86, p.636-638, June 1926).


Of it, Melotte wrote:

Faint nebula, 10'x 2'-5. A faint star (mag. 15.5) is at the centre, and another star (mag. 16) falls at the southern edge. The nebula is condensed towards the centre, and the southern half appears brighter than the northern. The star distribution in the surrounding area is irregular, the region on the following side being almost devoid of stars. The appearance of this nebula and of Barnards Nebula, N.G.C. 6822, is strikingly similar on the plates.

WLM, also cross-listed as MCG-3-1- 15 in the Morphological Catalog of Galaxies and PGC 143 in the Principal Galaxy Catalog, is a loner. Distance estimates place it at 3 million light years (930 kpc) from the Milky Way. Although WLM is isolated from other members of the Local Group, a study published in February 2022 suggests that it may be passing through some relatively dense intergalactic medium.


Structurally, the WLM Dwarf appears to be elongated in photos taken with the European Organization for Astronomical Research in the Southern Hemisphere's (ESO's) 3.5-meter New Technology Telescope (NTT). These high-resolution images clearly show individual stars across the galaxys full disk as well as a halo of very old stars surrounding that disk.


The fact that this halo exists is surprising for two reasons. First, it shows that the galaxy is older than previously thought; perhaps as old as the Milky Way itself. It also proves that a halo can also form around a dwarf galaxy in the first place. More often than not, such halos are reserved for far more massive galaxies. Adding to the mystery is the fact that the stars in the WLM halo appear much redder than the ones in the galaxy's central disk. That would seem to indicate that they are also much older. How is it that stars in a galaxy's halo formed before those in the galaxy itself?


Just last month, a close-up image of WLM taken by the James Webb Space Telescope (JWST) was released. Rather than view the entire galaxy, it focused on a small portion to reveal myriad individual stars as well as several far more distant galaxies that just happen to be along the same line of sight. (A great video that "flies" you into the galaxy has been created using images taken by the Very Large Telescope [VLT] and the JWST.)  Astronomers are interested in WLM due to its remoteness. By being set apart from more massive galaxies in the Local Group, like M31 and the Milky Way, WLM hasnt been disturbed by external tidal forces. This makes it ideal for testing theories of galaxy formation and evolution.


Astronomers are also interested to learn why WLM's embedded nebulosity is so poor in chemical elements heavier than hydrogen. This makes is more like galaxies that formed in the early universe than the other, more evolved galaxies in the Local Group. It has been suggested that, while new stars continue to form within WLM, creating new heavier elements in the process, some of that material is blasted out of the galaxy by "galactic winds" caused by supernovae explosions.


Above: A wonderful image of WLM and WLM-1 taken with an Astro-Tech AT90EDT at f/6.7 and SBIG ST-8300M.

Credit: Dan Crowson. More details about the image can be found here.


The WLM Dwarf is 2.2° due west of 4.9-magnitude 6 Ceti and 56' northeast of 6.3-magnitude 1 Ceti. Starhoppers should use 2nd-magnitude Deneb Kaitos [Beta (β) Ceti] as a guide to find 6 Ceti; it lies 8° to 6's southeast. Look for the galaxy's faint glow just west of the halfway point between two widely separated 9th-magnitude stars. SAO 147053 is 27' to the galaxy's northeast, while SAO 147052 is 25' to its southeast. The stars's north-south orientation parallels the galaxy's long, slender disk, which through my 18-inch, offers little more than a soft, featureless glow. An arc of 12th- to 14th-magnitude stars appears to cradle the galaxy's western edge. Like IC 1613, WLM is going to require some eyepiece experimentation before an ideal combination is found. In my scope, a 17-mm eyepiece producing 121x and a 3.8-mm exit pupil worked best.


Finally, if you could see WLM, then you just might be able to nab its solitary globular cluster. Can you spot two faint points just west of the center of the galaxy's elongated disk? The northern star shines at 15th magnitude, while southern "star" is actually the 16th-magnitude globular. It's a daunting test for even the largest amateur apertures.


Earlier this autumn, CN'er Keith Rivich posted that through his 25-inch (63.5-cm) Dobsonian, WLM-1 "is also interesting visually. In most images it looks quite stellar, making you think you are going to see a starlike object. And at low power that is what you see. But as you go up in power you notice the globular starts taking on a granular appearance while the star next to it, GSC 5838:798 remains stellar. Very similar to observing M31's globs."


I would be very interested to hear how you make out with WLM and WLM-1. Post your comments in this column's discussion forum.


Do you have a favorite challenge object of your own? I'd love to hear about it, as well as how you did with this month's test. Contact me through my website or post to this month's discussion forum.


Until next year, remember that half of the fun is the thrill of the chase. Game on!

About the Author:

Phil Harrington writes the monthly Binocular Universe column in Astronomy magazine and is the author of 9 books on astronomy. Visit his web site at www.philharrington.net to learn more.

Phil Harrington's Cosmic Challenge is copyright 2022 by Philip S. Harrington.  All rights reserved. No reproduction, in whole or in part, beyond single copies for use by an individual, is permitted without written permission of the copyright holder.


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