If you’ve ever measured something twice, like the width of a doorway, and got two different answers, you know how annoying it can be. Now imagine you’re a physicist and what you’re measuring tells you basic things about the universe. There are many such examples. For example, we can’t seem to get consistent measurements of how long neutrons live outside the nucleus.
But some of these are the so-called ” Hubble constant, is a measure of how fast the universe is expanding. It was measured using information from the cosmic microwave background to obtain a single value. And when we measured it using the apparent distances to objects in our current universe, we got values that differed by about 10 percent. As far as anyone can tell, there’s nothing wrong with either measure, and there’s no obvious way to get consent.
Researchers have now made a third independent measurement of the universe’s expansion by tracking the behavior of the supernova through gravitational lensing. When first discovered, this lens produced four images of her as a supernova. But after some time, a fifth star appears, and its time dilation is affected by the expansion of the universe, the Hubble constant.
inconsistent constant
The Hubble constant is a measure of the expansion of the universe, as it has units of kilometers per second per megaparsec. That is, every second, every megaparsec of the universe expands by a constant kilometer. Another way to think about this is in terms of a relatively stationary object 1 megaparsec away. In other words, it moves a few kilometers away every second.
How many kilos? That is the question. Measurements of the cosmic microwave background using the Planck satellite yielded a value of 67 km/s Mpc. Results done by tracking a distant supernova yield a value of 73 km/s Mpc. I’m not sure why these measurements are different, or if there’s some technical issue I haven’t identified yet. However, it is considered to be an important open question.
New research includes a third method of measuring distance that is independent of the other two. It relies on gravitational lensing, where space-time distortions caused by massive objects act as lenses that magnify background objects. It is not a perfect optical quality lens, so there may be some distortion or unevenness. This causes light from background objects to take different paths to Earth, and a single object can appear in several different locations dispersed around the lens.
On a cosmological scale, these paths may require light to travel very different distances to reach Earth. And since light travels at a finite speed, it means we can see a single object the same way when viewed from different angles. times. Last year, for example, researchers identified a single Hubble Space Telescope image that captured the supernova at three different times after the explosion.
A new study focuses on a similar supernova first identified in 2014. Now called SN Lefsdal, named after the astronomer who first proposed using a lens explosion to make measurements. When first detected, distant SN Refsdal was lensed by her galaxy cluster called MACS J1149.6 + 2223, creating four different images of her. However, a study of the lens formed by MACS J1149.6+2223 quickly found that an additional image would be produced approximately one year later.
Those predictions turned out to be correct. Images taken in late 2015 identified his fifth image of the event, created by gravitational lensing.
