The citizen science app, now available in eight languages, uses public input to identify kilonovae, neutron star mergers that create black holes.

Are you interested in making astronomical discoveries and contributing to the search for black holes? If your answer is “Absolutely,” then BlackHoleFinder is the perfect app for you. 

BlackHoleFinder, available for Android and Apple devices, was launched by the Dutch Black Hole Consortium in a bid for the public to assist astronomers in finding astronomical events called kilonovae. These smashups, which occur between two incredibly dense stellar remnants called neutron stars, can birth new black holes. But their brief light can also be hard to pinpoint on the sky and distinguish from other events or even the light flashing off satellites or asteroids, which is where BlackHoleFinder — and you — come in.

The newest version of the app is now available in eight languages: English, Dutch, Spanish, Italian, Chinese, Polish, Bengali, and German (previously, the app was accessible only in the first two). This upgrade was announced in Cape Town, South Africa, during the 32nd International Astronomical Union General Assembly. 

You can find out more about BlackHoleFinder, including links to download the app for your device, at www.blackholefinder.org.

How to spot a kilonova

Multiple types of violent events in the cosmos that can lead to the creation of new objects. One example is a kilonova: When two neutron stars merge, it results in a massive explosion, an extremely bright flash of light, and, ultimately, a new stellar-mass black hole. 

Related: LIGO Detects a Neutron Star Merger

Kilonovae not only emit electromagnetic radiation (light), but also gravitational waves. The latter is how they are typically found, via detectors including the Laser Interferometer Gravitational-wave Observatory (LIGO) and Virgo.  

But gravitational waves don’t allow for precisely pinpointing a kilonova’s location, so astronomers try to use the optical light flash instead. The flash from a kilonova can be seen from Earth, day or night; however, it is short-lived. Its light lasts a few days — a week at most — which poses an issue for astronomers who want to follow up on the event using telescopes that require proposals and have a long wait for observing time. This is where BlackGEM comes in — it is an array of three optical telescopes recently added to the European Southern Observatory’s La Silla Observatory in Chile. One of BlackGEM’s major advantages is that it can be rapidly commanded to point at a specific area of the sky once a gravitational wave signal has been detected. 

This, however, produces a new problem: an abundance of visible candidates that could possibly be the kilonova. How do astronomers differentiate to determine which is the real event?

This is where citizen scientists and BlackHoleFinder come in.

It takes a village

After downloading the app, users receive BlackHoleFinder’s crash course on how to differentiate between real and fake (or, at least, non-kilonova) sources in astronomical images. The app provides thorough instructions and details on what a kilonova is expected to look like: a round shape approximately 5-10 pixels wide, brighter than the background. Various example images allow the user to establish a true understanding of what a real kilonova is expected to look like in comparison to other transient events that might appear in images — for example, light refecting off a satellite or asteroid. 

Other potential false detections include artifacts produced through interactions between the cameras and incoming cosmic rays, or even patterns introduced through data processing. Some are quite obvious, but others require extra attention before deciding their validity. And “even among these astronomical signals that are not due to the kilonova, there are events related to black holes,” said Radboud University’s Paul Groot in a press release.

Why not just use artificial intelligence (AI) to filter out the real signals from the fake? Astronomers do have AI algorithms to help with this, but it turns out, these still need some assistance: “People are still much better at identifying patterns than our algorithms,” said Steve Bloemen, BlackGEM project manager. So, by getting involved in the BlackHoleFinder community and sifting through the candidates, the public not only helps to lessen the load of data these scientists must analyze, but also trains AI software to improve future detectiion of astrophysical events.

Additinally, the director of Las Cumbres Observatory (LCO) director is allowing particularly skilled BlackHoleFinder users who suspect a particular source to trigger follow-up observations with the LCO network of 0.4-meter robotic telescopes. This is just one example of professional and amateur astronomers working together to improve the quality of the science for all.

The launch of the updated BlackHoleFinder app will allow even more users to help astronomers save time and contribute to the advancement of our understanding of how neutron stars merge and birth new black holes. New data is available on the app just 15 minutes after it’s captured by BlackGEM, so you’ll never have to worry about running out of candidates to analyze.