Astronomers See Evidence of Something Unexpected in the Universe

Evidence for New Physics in the Universe

These Hubble Space Telescope images showcase two of the 19 galaxies analyzed in a project to improve the precision of the universe’s expansion rate, a value known as the Hubble constant. The color-composite images show NGC 3972 (left) and NGC 1015 (right), located 65 million light-years and 118 million light-years, respectively, from Earth. The yellow circles in each galaxy represent the locations of pulsating stars called Cepheid variables. Credit: NASA, ESA, A. Riess (STScI/JHU)

Astronomers have used NASA’s Hubble Space Telescope to make the most precise measurements of the expansion rate of the universe since it was first calculated nearly a century ago. Intriguingly, the results are forcing astronomers to consider that they may be seeing evidence of something unexpected at work in the universe.

That’s because the latest Hubble finding confirms a nagging discrepancy showing the universe to be expanding faster now than was expected from its trajectory seen shortly after the big bang. Researchers suggest that there may be new physics to explain the inconsistency.

“The community is really grappling with understanding the meaning of this discrepancy,” said lead researcher and Nobel Laureate Adam Riess of the Space Telescope Science Institute (STScI) and Johns Hopkins University, both in Baltimore, Maryland.

This illustration shows three steps astronomers used to measure the universe’s expansion rate (Hubble constant) to an unprecedented accuracy, reducing the total uncertainty to 2.3 percent. The measurements streamline and strengthen the construction of the cosmic distance ladder, which is used to measure accurate distances to galaxies near to and far from Earth. The latest Hubble study extends the number of Cepheid variable stars analyzed to distances of up to 10 times farther across our galaxy than previous Hubble results. Credit: NASA, ESA, A. Feild (STScI), and A. Riess (STScI/JHU)

Riess’s team, which includes Stefano Casertano, also of STScI and Johns Hopkins, has been using Hubble over the past six years to refine the measurements of the distances to galaxies, using their stars as milepost markers. Those measurements are used to calculate how fast the universe expands with time, a value known as the Hubble constant. The team’s new study extends the number of stars analyzed to distances up to 10 times farther into space than previous Hubble results.

But Riess’s value reinforces the disparity with the expected value derived from observations of the early universe’s expansion, 378,000 years after the big bang — the violent event that created the universe roughly 13.8 billion years ago. Those measurements were made by the European Space Agency’s Planck satellite, which maps the cosmic microwave background, a relic of the big bang. The difference between the two values is about 9 percent. The new Hubble measurements help reduce the chance that the discrepancy in the values is a coincidence to 1 in 5,000.

Planck’s result predicted that the Hubble constant value should now be 67 kilometers per second per megaparsec (3.3 million light-years), and could be no higher than 69 kilometers per second per megaparsec. This means that for every 3.3 million light-years farther away a galaxy is from us, it is moving 67 kilometers per second faster. But Riess’s team measured a value of 73 kilometers per second per megaparsec, indicating galaxies are moving at a faster rate than implied by observations of the early universe.

The Hubble data are so precise that astronomers cannot dismiss the gap between the two results as errors in any single measurement or method. “Both results have been tested multiple ways, so barring a series of unrelated mistakes,” Riess explained, “it is increasingly likely that this is not a bug but a feature of the universe.”

Explaining a Vexing Discrepancy

Riess outlined a few possible explanations for the mismatch, all related to the 95 percent of the universe that is shrouded in darkness. One possibility is that dark energy, already known to be accelerating the cosmos, may be shoving galaxies away from each other with even greater — or growing — strength. This means that the acceleration itself might not have a constant value in the universe but changes over time in the universe. Riess shared a Nobel Prize for the 1998 discovery of the accelerating universe.

Another idea is that the universe contains a new subatomic particle that travels close to the speed of light. Such speedy particles are collectively called “dark radiation” and include previously-known particles like neutrinos, which are created in nuclear reactions and radioactive decays. Unlike a normal neutrino, which interacts by a subatomic force, this new particle would be affected only by gravity and is dubbed a “sterile neutrino.”

Yet another attractive possibility is that dark matter (an invisible form of matter not made up of protons, neutrons, and electrons) interacts more strongly with normal matter or radiation than previously assumed.

Any of these scenarios would change the contents of the early universe, leading to inconsistencies in theoretical models. These inconsistencies would result in an incorrect value for the Hubble constant, inferred from observations of the young cosmos. This value would then be at odds with the number derived from the Hubble observations.

Riess and his colleagues don’t have any answers yet to this vexing problem, but his team will continue to work on fine-tuning the universe’s expansion rate. So far, Riess’s team, called the Supernova H0 for the Equation of State (SH0ES), has decreased the uncertainty to 2.3 percent. Before Hubble was launched in 1990, estimates of the Hubble constant varied by a factor of two. One of Hubble’s key goals was to help astronomers reduce the value of this uncertainty to within an error of only 10 percent. Since 2005, the group has been on a quest to refine the accuracy of the Hubble constant to a precision that allows for a better understanding of the universe’s behavior.

Building a Strong Distance Ladder

The team has been successful in refining the Hubble constant value by streamlining and strengthening the construction of the cosmic distance ladder, which the astronomers use to measure accurate distances to galaxies near to and far from Earth. The researchers have compared those distances with the expansion of space as measured by the stretching of light from receding galaxies. They then have used the apparent outward velocity of galaxies at each distance to calculate the Hubble constant.

But the Hubble constant’s value is only as precise as the accuracy of the measurements. Astronomers cannot use a tape measure to gauge the distances between galaxies. Instead, they have selected special classes of stars and supernovae as cosmic yardsticks or milepost markers to precisely measure galactic distances.

Among the most reliable for shorter distances are Cepheid variables, pulsating stars that brighten and dim at rates that correspond to their intrinsic brightness. Their distances, therefore, can be inferred by comparing their intrinsic brightness with their apparent brightness as seen from Earth.

Astronomer Henrietta Leavitt was the first to recognize the utility of Cepheid variables to gauge distances in 1913. But the first step is to measure the distances to Cepheids independent of their brightness, using a basic tool of geometry called parallax. Parallax is the apparent shift of an object’s position due to a change in an observer’s point of view. This technique was invented by the ancient Greeks who used it to measure the distance from Earth to the Moon.

The latest Hubble result is based on measurements of the parallax of eight newly analyzed Cepheids in our Milky Way galaxy. These stars are about 10 times farther away than any studied previously, residing between 6,000 light-years and 12,000 light-years from Earth, making them more challenging to measure. They pulsate at longer intervals, just like the Cepheids observed by Hubble in distant galaxies containing another reliable yardstick, exploding stars called Type Ia supernovae. This type of supernova flares with uniform brightness and is brilliant enough to be seen from relatively farther away. Previous Hubble observations studied 10 faster-blinking Cepheids located 300 light-years to 1,600 light-years from Earth.

Scanning the Stars

To measure parallax with Hubble, the team had to gauge the apparent tiny wobble of the Cepheids due to Earth’s motion around the Sun. These wobbles are the size of just 1/100 of a single pixel on the telescope’s camera, which is roughly the apparent size of a grain of sand seen 100 miles away.

Therefore, to ensure the accuracy of the measurements, the astronomers developed a clever method that was not envisioned when Hubble was launched. The researchers invented a scanning technique in which the telescope measured a star’s position a thousand times a minute every six months for four years.

The team calibrated the true brightness of the eight slowly pulsating stars and cross-correlated them with their more distant blinking cousins to tighten the inaccuracies in their distance ladder. The researchers then compared the brightness of the Cepheids and supernovae in those galaxies with better confidence, so they could more accurately measure the stars’ true brightness, and therefore calculate distances to hundreds of supernovae in far-flung galaxies with more precision.

Another advantage to this study is that the team used the same instrument, Hubble’s Wide Field Camera 3, to calibrate the luminosities of both the nearby Cepheids and those in other galaxies, eliminating the systematic errors that are almost unavoidably introduced by comparing those measurements from different telescopes.

“Ordinarily, if every six months you try to measure the change in position of one star relative to another at these distances, you are limited by your ability to figure out exactly where the star is,” Casertano explained. Using the new technique, Hubble slowly slews across a stellar target, and captures the image as a streak of light. “This method allows for repeated opportunities to measure the extremely tiny displacements due to parallax,” Riess added. “You’re measuring the separation between two stars, not just in one place on the camera, but over and over thousands of times, reducing the errors in measurement.”

The team’s goal is to further reduce the uncertainty by using data from Hubble and the European Space Agency’s Gaia space observatory, which will measure the positions and distances of stars with unprecedented precision. “This precision is what it will take to diagnose the cause of this discrepancy,” Casertano said.

The team’s results have been accepted for publication by The Astrophysical Journal.

Paper: New Parallaxes of Galactic Cepheids from Spatially Scanning the Hubble Space Telescope: Implications for the Hubble Constant


View Comments

  • If we believe that our World has started sometimes ago we are still in the position to decide which hypothesis, Lemaître’s or Gamow’s was closer to reality. There is an opinion that the problems in the standard cosmology could be solved by adjusting of details. Our suggestion is that we have to go back to the conceptions and use the observations accumulated since.

  • First thing first, get all fundamental scientific theories on the right footing are truly important step before we chart our future development of sciences. Einstein's famous equation is wrong otherwise garbage also can be used to make atomic bombs as long as it is matter or it has mass. Fortunately this is not the case. Precisely one must have photons before one can emit out photons. Photons are particles that have mass and dynamic photons possess momentum. Energy and matter cannot interchange to one another.
    Shamed to say that quantum scientists still don't seem to understand what is light correctly as they all still believe that light is oscillating electric and magnetic fields that are perpendicular to one another. Please get the basic understanding of light right first before we analyze data from Hubble telescope. If the foundation of current sciences is wrong and we can get even more wrong from here. It's still not too late to turn back now if we know that we are heading to the wrong directions.
    Big Bang is real, somehow we must able to explain what causes such gigantic explosion since Einstein's famous equation is wrong and not true. We somehow agree that there was dramatic expansion as a result of Big Bang explosion shortly after Big Bang which was much faster than any other phases of expansion of the universe.
    We knew the existence of gravitational forces among all celestial bodies within the universe. Expansion would naturally need some energy to do work against gravitational pulls among all celestial bodies. Energy cannot be created nor destroyed, and if energy would be consumed to do work against expansion, then logically the expansion of the universe must be slowed down gradually. Frankly, please get you basic correct first may be this would lead us to understand the data from Hubble telescope better and correctly before we jump to "unlearned" conclusion that we need new sciences to understand this seemingly impossible phenomenon that is the expansion of the universe now were getting even faster than before.
    I urge all scientists get their basics correct first before they jump to conclusion in producing illogical new scientific theories to "wrong" data.

    • What you are doing is kicking other people's god with your statement. I have found that this just makes the audience classify you as crazy. What you state is true. The problem is that professors at Universities around the world are more concerned with keeping their job and getting their children into a good University. They do not want to lose the prestige of being the top person in their field and they really do not want to have to learn an entirely new system. So what they do is get people like you to be discharged from the University. I have known that the paradigm is flawed for well over 20 years and have written a different theory that is incomplete. The problem comes with ethics. The weapons that humans will be able to build with the proper paradigm will make nuclear bombs look like birthday candles. Would you had a loaded shotgun to a 3 year old child? Further. I have been warned twice to keep my mouth shut.

  • The much larger question is not the how but why. This question is far more interesting because you can't have a Universe without knowing original causation. Random events shrouded in theory and hopeless understanding of what we can see and calculate is empty unless we know such things as why was their a Universe to begin with then suddenly it exists. In other words, put aside trying to explain what we can see and measure then draw conclusions in terms of science and math. We are limited in ever understanding two fundamental questions: What came before the Big Bang even if there was an original event, and two is there a limit to the size of a half-baked reality of what we call the Universe? In other words, nothing can be made from nothing and two a wall or barrier makes no sense whatsoever. I would love to be in the first row of a drama about a Universe and the midgets of mentality debating and calculating their world they call the Universe. Heed the words of Isaac Newton who once said "my observations and conclusions about natural philosophy (science and math in modern terms) is like a mysterious pebble found in an unlimited shoreline of a vast ocean containing the answers I will never obtain." He in fact has come the closest with his. Philosophiæ Naturalis Principia Mathematica. Our modern cosmologists are now sitting on that shoreline and perhaps have found a few more pebbles in this vast ocean still yet to be discovered. You have failed and you will continue to fail but the good news is just enjoy those few pebbles you have found because that is all you will find. Hopefully you will make a living wage along the way.

  • Photons directed toward you are light energy.
    Photons directed away from you are dark energy.
    The sun lights our planet and we can see the sun's rays.
    The far side of the sun also emits light but we don't see it that "energy."
    All star light works the same way. That's lots of dark energy.

    • Edit:
      Photons directed toward you are light energy.
      Photons directed away from you are dark energy.
      The sun lights our planet and we see the sun’s rays.
      The far side of the sun also emits light but we don’t see that “energy.”
      All star light works the same way. That’s lots of dark energy.

  • Understanding the universe is as vast and limitless as universe it self, we will continue to find another pebble. The physics of the universe is never constant and always ever changing.

  • the space/time do not move anywhere; it is as is now and always has been the same, as there were no 'time' compononent of space at the very end and at the very begining of the explosion of bigbang. There is a zone that is very similar to the number 0. it is us 'seeing' new parts of already established universe at 0 point. as we see new more parts of universe, it appears us that the universe is expanding within the 0 point of single dimentional universe

    • Bigbang could have only four states, not exploded, exploded, exploding right 'now' and all together happening at once. Based on the existance of time and other things, todays science strongly confirms that it has exploded; yet, this confirmation does not exclude the possibility, or probability, of the last two states. We may stuck into the '0' point of bigbang that enables both determinizm and caos alltogether. Time/space may not be going forward but repeating itself similar to concomitant mirror images. The remaing is the 'observation effect.'

  • There is real science and then there are climate science and astrophysics.
    Let us put into perspective how badly astrophysics is right now. They create black holes to explain the speed at which stars in the center of our galaxy move, they move too fast. Then they create dark matter to account for how stars are moving too fast further away from the center of the galaxy. Two fudge factors for the same observed discrepancy of their beloved relativity theory. And then they notice that light from distant objects has a stretched and red shifted. And the further away the light is, the more stretched and red shifted it is. Instead of imagining that the act of travelling millions and billions of light years might have some kind of drag on the light, they jump to the conclusion that the universe is accelerating its expansion, and have to make up yet another fudge factor, dark energy which is able to push galaxies apart at ever increasing rates, but cannot effect anything within a galaxy. Matter can neither be created nor destroyed, just changed in form, but we are then told in the same breath that the vacuum force of empty space is creating billions of subatomic particles which nearly immediately disappear.

  • Mr. Riess, the Standard Model of Particle Physics is wrong because it assumes there are only 4 Forces. I am the Discoverer of the 5th Force, and this occurred in Dec 1977 during a temporary reversal of fields. This 5th Force is a repelling, powerful, and non-mutual Force that occurred over a distance of 8 feet. In reading recent Astronomy literature, I have seen a manifestation of this 5th Force when it was reported that 2 Neutron Stars were orbiting each other, when suddenly one of those 2 Neutron Stars was repelled at great acceleration ! I have documented my Dec 1977 Discovery of the 5th Force in my self-publication of my Autobiography published in June 2012; it is available from a Ad in the Los Angeles, CA area; if you are interested in obtaining my Autobiography, please request it of me. Feb 24, 2018 .

Donna Weaver / Ray Villard, Space Telescope Science Institute

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