Cases & Voices

Borned in Venezuela, graduated in Physics from the University of Los Andes and PhD in Astrophysics from Yale University, Kathy Vivas works as a support astronomer at the Cerro Tololo Inter American Observatory, in La Serena, Chile. And it was from there that Vivas, along with a large team of scientists scattered around the world, participated in the project that resulted in the earliest observations of a ‘kilonova’: the fusion of two neutron stars 130 million years ago in the galaxy NGC4993, constellation of Hydra. We talked with her about the importance of this collaboration and how the work was carried out.

What was your participation in the research that led to the capture of light and gravitational waves from the star explosion? How this collaboration was developed?
My research area is not gravitational waves, but I got involved in the project for other reasons. Within my work at the Inter-American Observatory of Cerro Tololo, I’m part of the Support Team of the Dark Energy Chamber (DECam), a large field of vision instrument that is installed in the 4m Blanco telescope. A team of astronomers led by Edo Berger (Harvard-Smithsonian Center for Astrophysics, USA), in collaboration with the Dark Energy Survey (DES) team, identified DECam as the ideal instrument to identify the optical counterparts of gravitational wave events due to the great capacity of this instrument to cover large areas of the sky in a short time. The uncertainty in the position of the gravitational wave events that LIGO and VIRGO can give is great, of several degrees squares of the sky and for that reason it is fundamental to observe with optical instruments all the possible zone, to identify the object that has undergone a significant change in its brightness. Berger’s and DES’ project of using DECam for this purpose was approved months before under the special condition of "Target of Opportunity" or ToO. This means that when an event arises, Berger could request interruptions in any program that was being runned on the telescope to make his observations. As part of the Cerro Tololo team, we created the protocols for this to happen and we were ready to receive the alerts that could come from Ligo at any time.

And so it was. On August 17, during the day, Berger notified the Observatory on this event and when the night came, the Blanco and DECam telescopes were already looking for the optical counterpart. And indeed, the position of the source of the gravitational waves (the kilonova in NGC 4993) was clearly identified in the DECam data. It identified the source independently (other observatories also identified this using different techniques).

It was clear to everyone involved that this was a special event and that we should follow it closely. From the second night, the strategy of observation with DECam was changed. It was no longer necessary to cover a large area of the sky, we only had to observe the kilonova to study its evolution over time.

I was assigned to observe (for another project) the night of August 21 at the Blanco telescope five days after the first event. The first hour of observation that night was dedicated to observing the kilonova, in several filters. We watched it for as long as possible until, at last, it hid on the horizon. It was amazing to see "live" the rapid changes that occurred in the supernova. By day five, it was basically no longer visible in ultraviolet light, and its brightness in other redder photometric bands decreased considerably. So I returned to the telescope at the end of August, approximately two weeks after the event. We returned to make observations on the kilonova, but it was too weak to be detected with this telescope. The optical event had a very short life, of less than two weeks.

How was the experience of participating in a collective effort with such a great result?
It was really a very rewarding experience. Even though it was not my field of research, I knew I was participating in a groundbreaking discovery for physics and astronomy, and I am very happy to have contributed with a 'little grain of sand' in this collective effort.

What was the importance of collaborative work and advanced academic networks to the success of the initiative?
This event made it very clear that it is necessary to have great teams to achieve great things. Coordinated work was vital not to waste resources and to get the most out of the event. Advanced Internet Networks played a key role in this context: the images obtained in Chile were being analyzed in real time by different groups around the world.

Do you think that this discovery opens up new possibilities of work and participation for Latin American researchers?
Certainly. I think a new era in Astronomy is starting, which requires input from many work fronts, including theoretical work, modeling, big data, observations, etc. In this time of globalized and highly collaborative science, this is a great opportunity for Latin American researchers.

Read More:

• Chronicle of a global collaboration: the fusion of two neutron stars, a hug of 130 million years
• “La persecusión de una KiloNova”, por Luis Núñez: https://halley.uis.edu.co/clases/lnunez/
• Enrique Zas, physicist: "It is an event that marks the beginning of a new form of observation"
• LIGO publication: https://www.ligo.caltech.edu/page/press-release-gw170817
• Pierre Auger publication: https://www.auger.org/index.php/news/latest-news/the-pierre-auger-antares-and-icecube-observatories-team-up-for-a-search-of-neutrino-emission-from-the-binary-neutron-star-merger-gw170817
• ESO publication: https://www.eso.org/public/chile/news/eso1733/