IC 2497 is a spiral galaxy located about 650 million light-years distant in the small northern constellation of Leo Minor. Although similar in size to our Milky Way, it appears very small and faint due to its vast distance from us. At magnitude +15.8, this galaxy is beyond the reach of most amateur backyard scopes and seemingly just one of the many thousands of faint galaxies populating the night sky. However, a few years ago IC 2497 made international news not because of the galaxy itself, but due to a new strangle object that was discovered next to it - Hanny's Voorwerp.
In 2007, Dutch school teacher Hanny van Arkel signed up to the newly created on-line citizen science project Galaxy Zoo. The project enlisted help from the public to classify vast numbers of galaxies based on their physical appearance. The original dataset used was obtained from the Sloan Digital Sky Survey and contained almost 1 million galaxies. With so many galaxies it was thought that the analysis would take years, but the organisers were in for a pleasant surprise - within 24 hours the website was receiving almost 70,000 classifications an hour and the site even crashed temporarily due to intense traffic.
Within a few days of signing up Hanny van Arkel while classifying galaxy IC 2497 noticed a blue object just below the galaxy. She asked if anyone knew what it was, and nobody did. The new object became known as "Hanny's Voorwerp" - Voorwerp the Dutch word for object. It turns out to be a giant gas cloud located next to IC 2497, which is as large as the Milky Way and believed to have been illuminated 100,000 years or so ago by a powerful quasar event at the centre of the galaxy. From recent X-ray and light measurements it appears the quasar has at sometime within the last 70,000 years either "turned off" or even switched energy states and therefore no longer operating as it was. Whatever has happened, Hanny's Voorwerp and IC 2497 are incredibly interesting objects for professional astronomers.
Location and observing
IC 2497 is located in the western section of Leo Minor and close to the Lynx border. It's positioned 4 degrees directly east of α Lyn (mag. +3.1) and 0.5 degrees southwest of star 13 LMi (mag. +6.1). To spot it at least a 350mm (14-inch) aperture scope is recommended. In total, the galaxy spans just 0.6 x 0.3 arc minutes of apparent size and even with the largest amateur scopes, IC 2497 appears small, faint and lacking in detail.
If you think the galaxy is faint, the Voorwerp pushes this to another level. At about magnitude +19, it's incredibly dim. However, a few amateur astronomers with massive Dobsonian reflectors have managed to glimpse it as a ghostly glow hanging off the galaxy. It has been seen with scopes as small as 750mm (30-inch) in aperture!
IC 2497 Data Table
|Object Type||Spiral Galaxy|
|RA (J2000)||09h 41m 04s|
|DEC (J2000)||34d 43m 59s|
|Apparent Size (arc mins)||0.6 x 0.3|
|Number of Stars||400 Billion|
|Notable Feature||Hanny's Voorwerp|