- 3143 - UNIVERSE - rate of expansion? The disagreement over the Hubble constant of expansion is one of the biggest mysteries in cosmology today. In addition to helping us unravel this puzzle, the spacetime ripples from these cataclysmic events open a new window on the universe. We can anticipate many exciting discoveries in the coming decade.
- ----------------------- 3143 - UNIVERSE - rate of expansion?
- The Universe is expanding about 49,000 miles per hour for every million lightyears distance. The further away a galaxy is away from us the faster it is receding way. When you get out to about 14 billion lightyears away the galaxies are receding so fast their light will never reach us.
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- But don’t think of it as the galaxy’s speed. Think of it as the volume of space that is expanding between us.
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- Studying the violent collisions of black holes and neutron stars may soon provide a new measurement of the Universe's expansion rate.
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- Our two current best ways of estimating the Universe's rate of expansion is measuring the brightness and speed of pulsating and exploding stars, and looking at fluctuations in radiation from the early Universe. They give very different answers, suggesting our theory of the Universe may be wrong.
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- A third type of measurement, looking at the explosions of light and ripples in the fabric of space caused by black hole-neutron star collisions, should help to resolve this disagreement and clarify whether our theory of the Universe needs rewriting.
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- This new study simulated 25,000 scenarios of black holes and neutron stars colliding, aiming to see how many would likely be detected by instruments on Earth.
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- The simulations found that, by 2030, instruments on Earth could sense ripples in space-time caused by up to 3,000 such collisions, and that for around 100 of these events, telescopes would also see accompanying explosions of light.
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- This simulation concluded that this would be enough data to provide a new, completely independent measurement of the Universe's rate of expansion, precise and reliable enough to confirm or deny the need for new physics.
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- A neutron star is a dead star, created when a very large star explodes and then collapses, and it is incredibly dense - typically 10 miles across but with a mass up to twice that of our Sun. Its collision with a black hole is a cataclysmic event, causing ripples of space-time, known as “gravitational waves‘, that we can now detect on Earth with observatories like LIGO and Virgo.
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- We have not yet detected light from these collisions. But advances in the sensitivity of equipment detecting gravitational waves, together with new detectors in India and Japan, will lead to a huge leap forward in terms of how many of these types of events we can detect.
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- To calculate the Universe's rate of expansion, known as the “Hubble constant“, astrophysicists need to know the distance of astronomical objects from Earth as well as the speed at which they are moving away. Analyzing gravitational waves tells us how far away a collision is, leaving the speed to be determined.
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- To tell how fast the galaxy hosting a collision is moving away, we look at the "redshift" of light, the wavelength of light produced by a source has been stretched by its motion. Explosions of light that may accompany these collisions would help us pinpoint the galaxy where the collision happened, allowing researchers to combine measurements of distance and measurements of redshift in that galaxy.
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- The disagreement over the Hubble constant of expansion is one of the biggest mysteries in cosmology today. In addition to helping us unravel this puzzle, the spacetime ripples from these cataclysmic events open a new window on the universe. We can anticipate many exciting discoveries in the coming decade.
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- Gravitational waves are detected at two observatories in the United States (the LIGO Labs), one in Italy (Virgo), and one in Japan (KAGRA). A fifth observatory, LIGO-India, is now under construction.
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- Our two best current estimates of the Universe's expansion are 67 kilometers per second per megaparsec (3.26 million light years) and 74 kilometers per second per megaparsec.
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- The first is derived from analyzing the cosmic microwave background, the radiation left over from the Big Bang, while the second comes from comparing stars at different distances from Earth - specifically Cepheids, which have variable brightness, and exploding stars called type 1a supernovae.
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- Astronomers need confirmation of the disagreement from completely independent observations. They believe these can be provided through black hole-neutron star collisions and sensitive gravity wave detection.
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- May 1, 2021 3143
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