Right in the middle of this image taken with the NASA/ESA Hubble Space Telescope, nestled among a smattering of distant stars and even more distant galaxies, lies the newly discovered dwarf galaxy known as Donatiello II. If you can’t quite discern Donatiello II’s clump of faint stars in this image, then you are in good company. Donatiello II is one of three newly discovered galaxies. All three were missed by an algorithm designed to search astronomical data for potential galaxy candidates. Even the best algorithms have their limitations when it comes to distinguishing very faint galaxies from individual stars and background noise. In such challenging situations, identification must be done the old-fashioned way – by a dedicated human trawling through the data themselves.
The data that enabled these discoveries was collected by the Dark Energy Survey (DES), an intense observation effort that spanned six years. Using DES data, amateur astronomer Giuseppe Donatiello made his discovery – three very faint galaxies, now named Donatiello II, III and IV, respectively. All three are satellites of the well-known Sculptor Galaxy (otherwise known as NGC 253), meaning that they are all bound gravitationally to their more massive companion.
A team of astronomers used Hubble in an independent search to obtain long-exposure images of several faint galaxies, including Donatiello II. With the Hubble images, they were able to confirm their target galaxies’ association with NGC 253, thereby providing both an independent confirmation of Donatiello’s discovery and this new image.
Text credit: European Space Agency (ESA)