Quickfire questions with the kilonova discoverer

Dr Eleonora Troja is an associate research scientist in the Department of Astronomy at the University of Maryland, and works primarily at the NASA Goddard Space Flight Center in the Astrophysics Science Division

What are the similarities between GRB150101B and GW170817?

We think that in both cases the jet was not pointing toward us, but was slightly tilted.

In all previous cases of GRB explosions the jet was always pointing straight toward us, and its light was outshining everything else. It was like someone pointing a flashlight straight into our eyes – we could not see anything else but the bright light.

In GRB150101B and GW170817 the different jets’ orientations caused the light to look dimmer for us, and this unveiled the other facets of a neutron star merger, including the kilonova.

What are the differences between the two sources?

GRB150101B was much farther away. A distance of 1.7 billion light years is over 1,000-times farther away than GW170817. Even if LIGO was operational at the time, the gravitational-wave signal from GRB150101B would have been too faint to be detected.

What does this discovery and analysis mean for our understanding for such enormous cosmic events?

It means that GW170817 and its bright kilonova were not extraordinary events, but members of a bigger family of explosions.

Since GW170817 looked so different from anything we had ever seen before we did not know whether it was an exotic explosion or a common one. Having another event resembling its properties makes us more confident that GW170817 was not a rare finding, and we will probably catch more members of the same family in the near future.