Hubble’s “Masterpiece”: The Most Accurate Measurement of the Universe’s Expansion
Hubble’s “Masterpiece”: The Most Accurate Measurement of the Universe’s Expansion.
NASA has released a huge new report that astronomers are calling Hubble’s “giant work.”
By analyzing 30 years of data from the famous space telescope, the new study provides the most precise measurement yet of how fast the universe is expanding.
Astronomers have known for a century that the universe is expanding, thanks to observed galaxies moving away from us — the farther away they are, the faster they are.
The speed at which they move, relative to their distance from Earth, is a number called the Hubble constant, and measuring this number is one of the main tasks of the space telescope of the same name.
To measure the Hubble constant, astronomers study the distance of an object whose brightness is known — so that the dimmer it appears, the further away it becomes.
For objects that are relatively close in or near our galaxy, this role is filled by Cepheids, a class of stars that pulse in predictable patterns.
For further distances, astronomers use so-called Type Ia supernovae — cosmic explosions with well-defined peaks in brightness.
Over the past few decades, measurements of these objects have allowed astronomers to calculate the Hubble constant, which is about 70 kilometers (43.5 miles) per second per megagalaxy (/s/Mpc).
Essentially, a galaxy 1 megajoule (about 3.3 million light-years) away from Earth would be moving away at 70 kilometers per second, and for every 1 megajoule away, that speed would increase by 70 kilometers per second.
For this new study, a team of scientists has now collected and analyzed the most comprehensive catalog of these objects to date in order to make the most precise measurement of the Hubble constant to date.
This was done by studying 42 galaxies that contain both gobs and Type Ia supernovae captured by Hubble over the past 30 years.
“That’s what the Hubble Space Telescope was built for, using the best technology we know to do it,” said Adam Rees, the team’s lead scientist. Doubling this sample size would require Hubble to live another 30 years.”
The 36 galaxies imaged by Hubble all contain Cepheid stars and Type Ia supernovae, the two main markers used to calculate the Hubble constant.
From this work, the team calculated the Hubble constant to be 73 km/sec/Mpc (45.4 miles), with an error of just 1 km/sec/Mpc (0.6 miles).
This brings the uncertainty down to just 1.4%, far more precise than other measurement methods.
This new level of precision could help astronomers improve models of cosmology, including better estimates of the age of the universe and what might happen in its future.
“The Hubble constant is a very special number,” said cosmologist Dr Licia Verde, who was not involved in the study. “It can be used to thread the needle, from the past to the present, to test our understanding of the universe end-to-end. It requires a lot of meticulous work.”
However, a major mystery remains. The Standard Model of cosmology predicts that the Hubble constant should be much slower — about 67.5 km/s/Mpc (41.9 miles), which is also supported by observations of the background radiation left by the Big Bang.
The difference seems to come down to where we are in the universe — the constant is faster in our region and slower in the distant universe, even taking into account the known acceleration of expansion.
It sounds like the simplest explanation is that someone made a mistake, but oddly enough, both cases are pretty solid. Instead, astronomers suggest, new and unknown physics may be at work.
Thankfully, we may not have to wait too long to uncover new clues to this mystery — NASA’s upcoming James Webb Space Telescope will be able to study these same objects from farther distances and with higher resolution. landmark.
The research will be published in The Astrophysical Journal: