The biggest map of our galaxy just got revealed and it confirms the intriguing discrepancy in the value of the Hubble constant, further questioning our understanding of the expanding Universe.
Hubble’s constant – which is essentially a measure of the speed of the expanding universe – is determined by two different methods. One method looks at the early universe through the observation of the Cosmic Microwave Background (CMB) and the other method looks at the local universe through the light emitted by Cepheid variables.
In a recent news post, we described how Nobel laureate Adam Reiss and his team at the Space Telescope Science Institute determined a value for the Hubble constant 9% higher than that found by the CMB method. This value was found to an improved accuracy compared to previous studies and thus brings into question the reason for such a discrepancy.
Now with the help of Gaia, the European Space Agency (ESA) satellite, this accuracy has just been confirmed to an even greater accuracy!
The ESA Gaia satellite has been orbiting the Earth from 0.93 million miles away observing millions of stars every day for the last 36 months. This latest set of data is from the last 22 months where it observed 1.7 billion stars up to 8000 light-years away – that’s 50,000 trillion miles away. Not only did this create the largest 3D map of our galaxy, it also allowed Reiss and his team access to significantly more Cepheid variables to analyze. This gave them an even greater accuracy of 1 in 7000 compared to 1 in 1000.
However, now we are left with the same questions: what is it that causes this discrepancy? Dark energy, dark radiation, and/or dark matter? Do we need to revisit our understanding on the expansion of the universe?
The CMB is the oldest relic of our Universe whereas Cepheid variables and Type 1a supernovae are much younger than the CMB, so a clue could be in the age of the object that the measurement is being made from? Maybe a unified picture can help us to solve this mystery. Keep watching this space!