Full GOTO-North node under the skies of La Palma. Credit: K Ulaczyk (2024).

An 8.5 mag amplitude dwarf nova has been identified in real time by amateur astronomers via the Kilonova Seekers.

Previously described as playing astronomical ‘spot the difference,’ Kilonova Seekers asks the public to compare the latest images of a section of night sky to an image of the same section of space taken on previous nights.

Their goal – to spot new stars or significant changes in light intensity that may indicate that something remarkable has happened in space.

The project has now announced its first published major discovery – a bright exploding star.

The object underwent an extreme brightening (increasing by 2,500 times) that was not seen when compared to the image taken two days earlier.

The quick response and diligent work of the public allowed the object to be studied and classified early in its evolution, identifying it as a cataclysmic variable star, and given the name GOTO0650.

Co-lead of Kilonova Seekers, Dr Tom Killestein, Warwick Prize Fellow in the Astronomy and Astrophysics group, University of Warwick said: “Kilonova Seekers is a unique opportunity for members of the public to take part in true real-time astrophysics.

“Remarkably, public volunteers identified this star as an object of interest within three and a half hours of the image being taken by the GOTO telescopes – this discovery could have been missed among many other objects without their efforts.” 

He added: “The involvement of the volunteers didn’t stop there, as there was a huge follow-up response from the public.

“It was flagged for further observations from the Swift and Einstein Probe space observatories, and GOTO0650 was bright enough for amateur astronomers to take impressively high-quality observations of with their own equipment, which formed a key part of the paper and really helping us understand the object.” 

The discovery image that the Kilonova Seekers volunteers first saw of GOTO0650 when it went into outburst. The science, reference, and difference images are shown: the ‘science’ image taken on the night of discovery, the ‘reference’ image taken a few months prior under the best sky conditions, and the ‘difference’ image which uses an algorithm to subtract out all objects which have not changed in brightness between the science and reference. The very bright star in both the science and difference images is the object itself – it brightened by about a factor 2500x. Image credit: GOTO, T Killestein, University of Warwick.

Explosive outburst

Cataclysmic variable stars sporadically increase in brightness by large amounts before dropping back to normal levels.

They are compact binary star systems, consisting of a white dwarf star stealing matter from its companion donor star.

Periodically, material from the donor star hits a critical density and temperature within the disc of gas that surrounds the white dwarf, which causes an explosive outburst and bright flashes of light. 

The fast response of the public enabled the team to get an unusually highly complete dataset on the star, including spectroscopy, X-ray, and UV measurements, supplemented by the impressively high-quality observations of the amateur astronomers.

These observations suggest it is a period bouncer, the final state of a cataclysmic variable star, and a rare object to find even in the age of widespread wide-field imaging surveys. 

Co-lead of Kilonova Seekers, Dr Lisa Kelsey, Leverhulme Early Career Fellow, Institute of Astronomy and Kavli Institute for Cosmology, Cambridge said: “Citizen science is a powerful way to make novel serendipitous discoveries in vast datasets that would normally need to be analysed in depth by scientists. 

“With over 2.8 million classifications so far, the discovery of GOTO0650 is really the pinnacle of two years of consistent hard work from our volunteers.

“Without the Kilonova Seekers volunteers flagging this object, rapid follow-up would not have been possible, and this object may have been missed entirely.” 

An example of amateur observer image of GOTO0650 used to assist the identification and follow up observation of the object. Credit – Robin Leadbeater, Three Hills Observatory – http://www.threehillsobservatory.co.uk/astro/observatory/observatory.htm.

All-sky survey

The Kilonova Seekers Project is approaching its two-year anniversary of inviting members of the public to analyse near real-time data collected from the Warwick-led Gravitational-wave Optical Transient Observer (GOTO) project.

This project takes all-sky survey images of space from two arrays of telescopes located on opposite sides of the planet – in Spain and Australia.  

The vast numbers of observations taken in these imaging surveys will soon be beyond the capacity of individual and small teams of scientists to label and validate.

Citizen Science is a viable, mutually beneficial solution to avoid objects like GOTO0650 being missed.  

As a shining example of such efforts, Kilonova Seekers has provided over 3,500 members of the public with the opportunity to discover supernovae and variable stars using real data.

With volunteers from around the world, there is almost always someone online looking at the data in real time. 

The findings are published in Astronomy & Astrophysics.