A project enabling volunteers to help professional astronomers find supernovae has achieved success within a week of launching. Dr Brad Tucker of the Australian National University described the first discovery as “perfect in its boringness”, while being exciting for the speed with which it was found.
The explosion in question is a Type Ia supernova that went off in a galaxy 970 million light-years away. The explosion predated the emergence of complex life on Earth, but the light has only reached us now, in time to be picked up by the SkyMapper 1.3-meter (4.3 feet) telescope. A comparison of an image taken a few days ago and an old one of the same galaxy caused a computer program to recognize a difference.
The comparison, along with many others, was placed on the citizen science portal Zooniverse, where three amateurs marked it as a likely supernova. SkyMapper followed up and confirmed that not only is the light a supernova, but it is just the sort they were looking for, all with the speed needed to properly track the star's decline.
Unlike those who discover comets, supernova discoverers do not get their names immortalized, with the object in question dubbed SN2017dxh, but the finders will have their names submitted to the International Astronomical Union.
In the week since Tucker and the SkyMapper team started putting potential supernovae on Zooinverse, seven other reasonably good prospects have been found, but Tucker told IFLScience these were yet to be confirmed, let alone categorized. At least 18 other prospects have been identified, but most are considered more likely to be false alarms.
The detections represent a new twist in the path of supernova discovery. Not long ago most of these giant explosions were found by amateurs. Then big search projects like SkyMapper superseded them, until the realization came that more data was being produced than the professionals could handle.
Supernovae represent an important opportunity to learn about the universe. Some are valued for being close enough to give us an exceptional view, while new and exotic types can teach us about the nature of stars. For many astronomers, however, the greatest value lies in type Ia supernovae, which have the exceptionally useful trait of being consistent in their intrinsic brightness, allowing us to measure their distance based on how bright they appear. This at least is true of the most common forms of type Ias. Certain more unusual subgroups, while interesting for other reasons, are suspected of having different peak brightnesses and therefore mucking up the distance data. Thus Tucker's delight at a “boring” find.
The speed at which a supernova is moving away from us can be calculated from its redshift. Combined with the distance measurements this can be used to tell us how fast the universe is expanding, which in turn provides a measure of dark energy. The larger the sample size, the more precise we can be on this question, including putting to rest the small minority of physicists who continue to question whether dark energy exists at all.
Supernovae are so bright they can outshine the entire galaxy in which they occur, but peak brightness does not last long. If we don't happen to have a telescope pointing in the right place at the right time we can miss it. Instead, it is possible to get a good idea of how bright the peak was through plotting the downward side of the light curve, but if we don't know there is a reason to be taking observations of the host galaxy we won't get sufficient data points in time.
Consequently, it is important to analyze possible supernova observations quickly, identifying priorities for follow-up images. Large numbers of potential supernovae sitings are collected, and about 80 percent can be ruled out using computer algorithms, being caused by flares from nearby variable stars or the passage of a known asteroid across a field of view.
However, for the other 20 percent, human eyes are needed. “We're not obsolete yet,” Tucker told IFLScience.
Astronomers are calling on amateur assistance through Zooniverse for more and more things, from finding planets around other stars to the search for Planet Nine. Tucker told IFLScience that so far, the number of people volunteering, and their willingness of many to engage in multiple searches, means old programs have not been left stranded as everyone rushes to the new cool thing. Nevertheless, more eyes are always welcome.
Skymapper is seeking supernovae across the southern hemisphere, which Tucker calls “the best half of the sky”. A matching program run by Pan-STARRS in the north that also relies on volunteers. Fortunately, given the population imbalance, many northern hemisphere residents are giving Skymapper assistance, with two of the three amateurs who discovered SN2017dxh coming from Belgium and Scotland.