New research suggests that a troubling difference in the universe’s expansion rate, known as the Hubble constant, may be caused by Earth’s location in a vast, low-density region of the universe.
This problem is called “Haber tension“This is because there are two ways to calculate Hubble constant exist The current age of the universebut these methods are not consistent.
The team behind the study believes the problem is because our galaxy, Milky Waylocated in lower-density areas or “supervoids.” This means that the space will Appear Expand faster in this “Harber Bubble” (officially known as the “Harber Bubble”) Keenan-Bugg-Cowie(KBC) Super Hollow (also somewhat unkindly called “local vulnerabilities”) thus distorting our observations.
“A void is a region in the universe that is less dense than average,” team member Indranil Banik, a cosmologist at the University of St. Andrews, told Space.com. “A supervoid is a void larger than about 300 million light-years.”
What is a supervoid?
this The universe is expanding At incredible speeds, but even though your commute to work might be seem Every day gets longer, which is just one noteworthy factor on the vast scale of the universe.
This means that the Hubble constant measures how fast distant galaxies are moving away from each other.
At first glance, this might seem to make differences in Hubble constant rates a less pressing issue. After all, it doesn’t affect how far you have to walk for your morning coffee.
The problem is that without understanding how fast the universe is expanding, cosmologists can’t understand how the universe is evolving, and our best model of that evolution is Lambda Cold Dark Matter (Lambda CDM), or the “Standard Model of Cosmology.” , is missing.
Therefore, the Hubble tension is certainly not something that scientists can solve or ignore.
The largest known supervoid in the universe is Eridanus Supervoidits width is 1.8 billion light-years, but the KBC supervoid is no slouch in terms of size.
“The KBC supervoid is a region about 20 percent less dense than the average density of the universe, roughly centered around where we are and extending out about 1 billion light-years,” Barnick said. “Usually, when people use distance and distance to measure the Hubble constant red shiftthey don’t get very far out because the expansion rate of the universe changes over time.
“This means that people typically don’t observe beyond 2 billion light-years. But it means that the observations are made within the spatial extent of the KBC.”
Why would observations inside the KBC supervoid produce enough of a difference in the Hubble constant to cause Hubble tension?
What is Haber tension?
There are two ways to calculate the Hubble tension; we call these “observation” and “theory” (although this is indeed an oversimplification).
Scientists started with theoretical methods and observed a kind of “cosmic fossil” called “cosmic fossil”. cosmic microwave background (China-Pakistan). The first light to travel across the universe, the cosmic microwave background (CMB), is a radiation field that fills the entire universe almost uniformly.
The scientists then turned the clock of the universe forward and modeled its evolution using Lambda CDM as a template. This gives them the current value of Hubble’s constant.
In the “observational” method, scientists use astronomical data to measure the distance to the galaxy Type Ia supernova Or variable stars, two examples of what astronomers call “standard candles.”
They can then calculate how fast these galaxies are receding by examining changes in the wavelength, or “redshift,” of the light emitted by these objects. The greater the redshift, the faster the galaxy is moving away from us, from which the Hubble constant can be calculated.
“The main thing to remember about the late universe is that as you look further out, you’re looking further back in time,” Barnick said. “Photons with longer travel times will be stretched more due to the expansion of the universe.”
The problem is that this observational method gives a value for the Hubble constant that is larger than the value obtained by forward extrapolation from Lambda CDM.
“Theoretical methods” give a value for the Hubble constant of about 152,000 miles per hour per megaparsec (68 kilometers per second per megaparsec, or Mpc), while “observational methods” usually give a higher value, somewhere between Between 157,000 mph per megaparsec and 157,000 mph per megaparsec.
One Mpc is equivalent to 3.26 light years Or 5.8 trillion miles (9.4 trillion kilometers), so the Hubble tension is obviously a huge difference.
“Late Universe observations tell us that the expansion rate is 10 percent faster than what we extrapolate from the conditions of the universe during the CMB to today using Lambda CDM,” Barnick said. “This is not the discovery one wants to make in our best cosmology. is wrong.
“That’s a problem, but nature doesn’t care about our theories!”
Banik and colleagues believe that the Hubble tension arises from the fact that the universe emerged Expand faster within the KBC Super Void.
“You can think of a supervoid as a uniform universe plus some concentrated negative mass,” Barnick said. “This has a repulsive gravitational effect that can redshift galaxies beyond what would be caused by the expansion of the universe alone.”
There is a difference because theoretical methods average the Hubble constant over the entire universe, while observational methods only calculate it within the KBC supervoid. Therefore, within this “Harber Bubble” we have a distorted and biased view.
“This would make the universe appear locally to be expanding faster than it actually is, which in turn could resolve the Hubble tension.”
Interestingly, when the team began investigating the KBC supervoid, they didn’t even consider Hubble’s tension. What they really want to know is whether supervoids like this appear in lambda clean development mechanism.
“That’s when we realized that if you were in the void, you’d think the universe was expanding faster than it actually is,” Barnick explained. “So, that’s when we also realized that this might solve Hubble’s problem. tension.”
As for whether super voids like “local voids” are possible in Lambda CDM, Banik said that the research team found that such a large and deep void is impossible to appear in the standard model of cosmology, at least from the current situation. That’s right.
Barnick predicts that a solution to the Hubble tension could come as early as 2030.
“It would be a big relief to know which aspects of standard cosmology need to be modified to resolve the Hubble tension. In fact, solving it requires deeper theory,” Banik concluded. “My point is, Haber tension will be resolved Within ten years.
“However, if I am wrong about what causes the Hubble tension, then solving it is absolutely impossible because there is no good runner-up theory that is consistent with other important constraints, such as the age of the oldest stars.”
The team’s research is published in the journal Monthly Notices of the Royal Astronomical Society.