A kilonova that occurred in 2017 transmitted gravitational waves and light throughout the universe. The delay in signal arrival was 1.7 seconds here on Earth. How come?
The idea that gravitational waves and light travel at the
same speed is a long-standing one in the field of astronomy and is based on
relativity.
But a fascinating contradiction has surfaced that calls into
question this basic belief. Earth was reached by gravitational waves over two
seconds ahead of light when the first neutron star-neutron star merger was
detected in both. This happened even though the signals were meant to be
travelling at the same pace and were coming from 130 million light-years away.
The incident in issue happened in the far-off galaxy NGC
4993 on August 17, 2017. Gravitational waves were released as the two neutron
stars spiralled closer to one another and rushed across curved space.
A magnificent flash of gamma rays followed their eventual
collision, with the gravitational wave signal ceasing 1.7 seconds later.
Scientists have been perplexed by this temporal gap since, if both signals were
moving at the same pace, they ought to have arrived simultaneously.
This delay has been explained by a number of theories. One
theory is that material was ejected from the collision and collided with nearby
matter before the light was released. According to a different explanation, the
light was produced inside the neutron stars and took some time to get to the
surface. According to a third theory, light had to travel through an
environment that was dense with stuff, which caused it to slow down.
This phenomenon has important ramifications for how we
perceive the cosmos. It calls into doubt whether gravity and light travel at
the same speeds or not. Neutron star mergers, which are thought to be the
cosmic factories for some of the heaviest elements in the universe, like gold
and platinum, now have new directions for study.
Scientists hope to improve their grasp of this perplexing
mismatch as they continue to collect more data on these cosmic events. As
things are right now, the mystery endures, acting as a sobering reminder of the
difficulties and unknowns that still face us in our quest to comprehend the
universe.
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