![\"\"\/](\"https:\/\/www.europesays.com\/uk\/wp-content\/uploads\/2025\/05\/HubbleTension_ComaCluster.jpeg\")
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\n\t\t\t\t\t\tThe Coma Cluster is a galaxy cluster composed of over 1,000 galaxies. The most recent distance measurement places the cluster 320 million light-years away, with an uncertainty of only 7 million light-years. Credit: NASA, ESA, J. Mack (STScI), and J. Madrid (Australian Telescope National Facility)\t\t\t\t\t<\/p>\n
A recent study<\/a> published in The Astrophysical Journal Letters has provided the most precise distance to the Coma Cluster of galaxies yet \u2014 and also has deepened a crisis in cosmology.<\/p>\n The problem is that when we look around the local universe, the universe seems to be expanding faster than predicted by the current models that govern physics. This gap between what models predict and what is actually observed has become known as the Hubble tension.<\/p>\n For years, the Hubble tension has been a vexing reminder to scientists that something is not quite right in their models. But with the new observations of the Coma Cluster \u2014 which lies practically in our own backyard by cosmological standards \u2014 scientists say the discrepancy stands out more glaringly than ever. \u201cThe tension now turns into a crisis,\u201d said the paper\u2019s first author, Daniel Scolnic of Duke University, in a press release<\/a>.<\/p>\n So, how fast is the universe expanding?<\/strong><\/p>\n Scolnic\u2019s new works expanded on a previous study released in 2024 that used data collected by the Dark Energy Spectroscopic Instrument (DESI) mounted to the Mayall Telescope in Kitt Peak, Arizona. The instrument\u2019s goal is to study the nature of the expansion of the universe by observing distant galaxies that are being carried away from us.<\/p>\n Scientists characterize a galaxy\u2019s distance based on how much of its light is shifted toward redder wavelengths due to the Doppler effect, called its redshift. Generally speaking, the faster a galaxy appears to be moving away from us, the farther from us it is. But to properly measure how quickly the universe is expanding, scientists need independent measurements of the distances to galaxies with alternative methods.<\/p>\n One such method is called the Fundamental Plane method. It applies to elliptical galaxies \u2014 older galaxies whose spiral structures have been erased by mergers. The method infers a galaxy\u2019s true size by looking at how bright it is and how broad the range of speeds is at which its stars move. When the true size is known, it\u2019s easy to calculate the true distance based on how large or small it appears.<\/p>\n The Fundamental Plane method is one of a variety of methods to calculate distances to galaxies. Together, they make up what scientists call the cosmic distance ladder; as astronomers look farther out, each method is anchored to a reference point established by the previous method.<\/p>\n The 2024 study from the DESI collaboration released a version of the Fundamental Plane method that was anchored to the known distance to the massive Coma Cluster \u2014 a nearby cluster filled with elliptical galaxies. From it, they calculated the universe\u2019s current expansion rate \u2014 known as the Hubble constant, or H0. They found a value of 76 kilometers per second per megaparsec \u2014 but with an uncertainty of nearly 5 km\/s\/Mpc due to the imprecision of the distance to the Coma Cluster.<\/p>\n Thus, the Coma Cluster served as an important reference: If astronomers could measure a more precise distance to the cluster, they could greatly improve their estimate of the expansion rate of the universe.\u00a0<\/p>\n \u201cWhen the DESI collaboration released their \u2026 paper, and I saw in the abstract how good their measurement could be if they just had one more piece, I got extremely excited, cause I knew I could help provide that piece,\u201d Scolnic tells Astronomy.\u00a0<\/p>\n A cosmological crisis<\/strong><\/p>\n That piece that Scolnic could provide was a better distance to the Coma Cluster using another independent method. In addition to being rich in elliptical galaxies, the Coma Cluster also has an abundance of Type Ia supernovae. These stellar explosions are referred to as \u201cstandard candles\u201d because physics dictates that they explode when white dwarf stars reach a critical mass, meaning their absolute brightnesses are well known. This means they can be used to reliably measure distances: The dimmer it appears, the farther away it is. Scolnic\u2019s team observed the light curves of 13 supernovae in the cluster and found the distance to the Coma Cluster to be around 320 million light-years, with an uncertainty of just 7 million light-years.<\/p>\n With that anchor point, astronomers refined the Fundamental Plane relation and derived a value for the Hubble constant of 76.5 kilometers per second per megaparsec with an uncertainty of just 2.2 km\/s\/Mpc \u2014 twice as precise as the DESI Collaboration\u2019s original value.<\/p>\n This value is an excellent match to other independent measurements of the Hubble constant that are based on looking at objects in the nearby universe.<\/p>\n But it only exacerbates the tension with the expansion rate predicted by the standard model of cosmology, known as the Lambda Cold Dark Model (\u039bCDM). To calculate the model\u2019s predictions, scientists begin with observations of the light radiated from after the Big Bang, known as the cosmic microwave background (CMB). Then, they use \u039bCDM to extrapolate forward through time. But this approach yields a present-day Hubble constant of only 67.4 km\/s\/Mpc<\/a>.<\/p>\n The new Coma Cluster distance measurement\u2019s solidification of the much higher value suggests that the root of the Hubble tension lies within \u039bCDM itself \u2014 not a error in measurement. \u201cWe\u2019re at a point where we\u2019re pressing really hard against the models we\u2019ve been using for two and a half decades, and we\u2019re seeing that things aren\u2019t matching up,\u201d Scolnic said in a press release<\/a>.<\/p>\n![\"\"](\"https:\/\/www.europesays.com\/uk\/wp-content\/uploads\/2025\/05\/HubbleTension_Raisinbread.gif\")
To conceptualize how galaxies behave in an expanding universe, you can use a simple thought experiment of baking raisin bread. Let\u2019s pretend each raisin represents a galaxy. When the dough is first placed in the oven, you start with two raisins 2 inch (5 centimeters) apart and another two that are 4 inches (10 cm) apart. But when the bread is done baking, the distance between those same berries have doubled. This analogy applies to galaxies moving away from each other as the cosmos itself expands. Credit: ScienceApologist\/Wikimedia Commons<\/p>\n![\"\"](\"https:\/\/www.europesays.com\/uk\/wp-content\/uploads\/2025\/05\/HubbleTension_Highway.jpg\")
A disjointed highway depicts the different measurements of the Hubble constant by different missions and methods, where the gap between the two is the Hubble tension. Acronyms and their meaning: the cosmic microwave background (CMB), Wilkinson Microwave Anisotropy Probe (WMAP), BAO (Baryonic Acoustic Oscillation (BAO), Big Bang (BB), Dark Energy Survey (DES), Lambda Cold Dark Matter (\u039bCDM), and tip of the red-giant branch (TRGB). Credit: NOIRLab\/NSF\/AURA\/J. da Silva\/Adam Riess<\/p>\n