The standard view of cosmic evolution may be challenged by the discovery of a huge galaxy that appears to lack dark matter. Dark matter, which makes up about 85% of the matter in the universe, is missing from NGC 1277, a galaxy in the Perseus galaxy cluster. The galaxy, located 240 million light-years from Earth, is the first Milky Way-sized cluster of stars, planets, dust, and gas to be found to lack dark matter.
Dark matter is effectively invisible because it doesn’t interact with light like the regular matter that makes up stars, planets, and us. However, its presence can be inferred from its gravitational interactions. The existence of this shadowy substance was first suggested when astronomers observed massive galaxies spinning so fast that they would fly apart if not for the gravitational pull of some invisible mass holding them together. The team’s research is published in the journal Astronomy and Astrophysics in 2023.
This fact led scientists to hypothesize that all large galaxies are surrounded by a shell of dark matter, and this has become an important assumption in developing theories of galaxy evolution. However, the discovery of a galaxy that apparently has no dark matter challenges this assumption.
A zoomed-out image of the galaxy NGC 1277 taken by the Hubble Space Telescope, which lies near the centre of the Perseus cluster of more than 1,000 galaxies, located 240 million light-years from Earth. Instituto de Astrofísica de Canarias/P. Kehusma/NASA/ESA
NGC 1277, considered a cosmic relic, is unique among galaxies in that it barely interacts with other galaxies around it. Such galaxies are thought to be the remnants of giant galaxies that existed in the early universe. As such, these relic galaxies play an important role in astronomers’ understanding of how the first galaxies formed.
To further this line of research, Cameron and his colleagues observed the relic galaxy NGC 1277 with an instrument called an integral field spectrograph. This allowed them to map the galaxy’s motion, determine its mass, and determine its distribution.
This showed that the distribution of the total mass of NGC 1277, which must include dark matter, matches the distribution of the mass of its normal matter, i.e. stars, dust, gas and planets. This means that within the radius of the galaxy, the content of dark matter cannot exceed 5%, but the results are more consistent with the assumption that there is no dark matter at all in NGC 1277.
This is surprising because currently accepted models of cosmic evolution, including the standard model of cosmology, suggest that NGC 1277 should be composed of 10–70% dark matter.
The illustration shows a typical galaxy shrouded in a dark matter halo, and NGC 1277, which lacks this mysterious form of matter. ESO 325-G004: NASA, ESA
The scientists behind the discovery have several ideas as to why NGC 1277 has so little dark matter. One hypothesis is that gravitational interactions with the environment within the galaxy cluster that contains it led to the expulsion of dark matter. A second hypothesis is that dark matter was expelled from the system when the galaxy formed through the merger of protogalactic fragments, resulting in the relic galaxy.
The team is not entirely satisfied with any of the explanations and will therefore continue to study NGC 1277 using the William Herschel Telescope (WHT) at the Roque de los Muchachos Observatory on the Canary Island of La Palma.
If future studies confirm that the relic galaxy is missing the most mysterious form of matter in the universe, the scientists believe that this will not cast doubt on the existence of dark matter. Instead, the team believes that it will cast doubt on alternative models of dark matter, so-called modified theories of gravity.
Dark matter in a particular galaxy can disappear, the modified law of universal gravitation must be universal; it cannot have exceptions. Therefore, a galaxy without dark matter is a refutation of this kind of alternative to dark matter.
New clues about the evolution of dark energy are part of one of the most detailed maps of the cosmos ever created, based on data collected in the first year by the Dark Energy Spectroscopic Survey Instrument (DESI). The instrument’s 5,000 robotic eyes collect light from millions of galaxies covering more than a third of the entire sky visible from Earth. That light is then broken down into a spectrum of colors, allowing scientists to measure the expansion of the universe over billions of years by measuring the change in the wavelength of light, called a “redshift.”
The current “standard model” of the cosmos, its history and evolution is called the lambda cold dark matter (LCDM) model, but the supremacy of this model, in which lambda represents the cosmological constant and dark energy, may now be under serious threat.
That’s because new observations of the cosmos suggest that dark energy, the force that’s causing our universe to expand faster and faster, appears to be weakening. That may not seem like much on its own, but the discovery could potentially lead to the first major paradigm shift in cosmology since the discovery of the universe’s accelerating expansion just over 25 years ago. It could even suggest that our universe will end not with a “Big Rip” or a “Big Cool,” but with a “Big Crunch.”
The LCDM model suggests that immediately after the Big Bang, the Universe was extremely dense and incredibly hot, but at the same time remarkably smooth and more or less the same or uniform in all directions.
As the universe expanded, small fluctuations in density began to form, and these dense regions grew. Clumps of dark matter began to condense as the universe evolved, and the newly formed atoms collected and stimulated the movement of gas molecules within these clumps. As a result, the universe ended up filled almost entirely with hydrogen and helium (the two lightest and simplest chemical elements) and dark matter.
The combination of electrons and protons to form the first atoms suddenly gave light the ability to travel freely, and this first light is now observed as the cosmic microwave background (CMB), a “fossil” radiation that can tell us much about the history of the universe.
The higher-density regions pulled in gas and dark matter, forming the seeds of the first galaxies in the LCDM model, which collapsed to form protogalaxies. In these early galaxies, hydrogen and helium formed the first stars. Eventually, the protogalaxies and the halos around them merged to form ever larger galaxies.
However, it is important to note that in this model, dark energy is represented by lambda. Lambda is assumed to be constant over time.
DESI found that the “equation of state” of the universe is not consistent with the conventional LCDM model, but instead indicates that dark energy changes over time. These results open a window for variable dark energy models, as they demonstrate a departure from a constant equation of state.
If these new DESI findings prove accurate (and they currently appear to be remarkably reliable), then the cosmological constant may no longer be an appropriate proxy for the mysterious force of dark energy.
In 1915, Albert Einstein put forward perhaps his most revolutionary theory, the general theory of relativity, which described gravity as a concept that arises from the curvature of space and time—a curvature caused by bodies with mass.
Two years later, in 1917, Einstein and the Dutch astronomer Willem de Sitter demonstrated that the equations of general relativity could be used to describe the universe, albeit in a simplified way. But there was a problem: the universe described by the equations of general relativity did not describe a universe at rest. The conventional wisdom in physics at the time was that the universe was static, neither expanding nor contracting, and Einstein agreed. So he added a kind of “factor” to his equations: the cosmological constant, or lambda.
This balanced the universe, adding the right amount of pull and push to keep it static.
About 12 years later, in 1929, Edwin Hubble was studying distant galaxies when he discovered that their light was stretched, or “redshifted.” He noticed that the farther away the galaxy, the stronger this effect was. This indicated that the universe was not static but was actually expanding. Scientists spent the next seven decades trying to measure the rate of this expansion, a value called the “Hubble constant.”
A long-exposure photograph shows star trails above the Earth. If the acceleration of the universe’s expansion remained constant over centuries, such images would be impossible. Maxim Senin
No longer needing to describe a static universe, Einstein dropped the cosmological constant from his equations of the universe, reportedly calling the introduction of lambda his “greatest mistake.” However, the cosmological constant did not remain in the cosmic scrap heap for long. By the end of the 20th century, lambda had returned in a big way, and in a new role.
In 1998, two separate teams of astronomers, observing distant Type 1a supernovae and using them to measure cosmic distances, discovered that the expansion of the universe is not actually slowing down, as one might expect. It is speeding up. Dark energy was then introduced as a proxy for what appeared to be the cause of this accelerating expansion.
In many models of the cosmos, including the popular LCDM model, dark energy is represented by a rescued cosmological constant, or lambda, which now opposes gravity and pushes apart the very fabric of space and time at an ever-increasing rate.
However, after the introduction of the cosmological constant as a quantity characterizing the accelerated expansion of space, it remained a problem. The values obtained as a result of observing distant supernovae and the value predicted by theories of quantum physics continue to differ greatly, diverging by as much as 10 to the power of 121 (a one with 121 zeros).
An illustration of the first year of data from the Dark Energy Spectroscopic Instrument (DESI), showing a section of the larger three-dimensional map that DESI is creating over the course of its five-year study. DESI Collaboration/KPNO/NOIRLab/NSF/AURA/P.Horálek/R.Proctor
There is one scenario in which, if dark energy is an unchanging cosmological constant, over billions of years all galaxies will move so far apart that the night sky above Earth will become empty. This could result in the universe becoming a cold cosmos made up of widely scattered dead galaxies, in the so-called “Big Chill” scenario. Alternatively, continued accelerated expansion could cause the fabric of spacetime itself to rip apart, in a scenario known as the “Big Rip.”
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But the new DESI map could point to a different cosmic fate, in which the universe collapses again, reaching the hot, dense state seen immediately after the Big Bang. If the results of the first year of DESI are correct, the universe’s accelerating expansion will stop and eventually reverse, and the universe could begin to contract under the influence of gravity. This could eventually lead to the universe collapsing in a “Big Crunch” scenario.
In the second and third years of DESI’s operation, scientists will study the distortions of space associated with redshift.
Hints about the evolution of dark energy, which makes up about 70% of the mass and energy of the universe, were first obtained in 2024 by the Dark Energy Spectroscopic Instrument (DESI). The discovery was shocking because the best description we have of the cosmos, the standard model of cosmology, or lambda cold dark matter (LCDM), predicts that dark energy should be constant over time.
New results from 2025, provided by the Supernova Cosmology Project and including 2,087 detonating vampire stars, also called standardized Type 1a supernovae, provide another line of evidence that dark energy is not constant and that the LCDM may need to be revised.
If dark energy weakens, it will have implications for our understanding of how the cosmos will end.
Supernova 1994D near the galaxy NGC 4526. NASA, ESA, The Hubble Key Project Team and The High-Z Supernova Search Team
Type 1a supernovae are stellar remnants called white dwarfs, which are left behind when sun-sized stars die. In tight binary partnerships with other stars, these stellar corpses can steal matter like a cosmic vampire.
This material accumulates on the white dwarf until the dead star’s mass exceeds the so-called Chandrasekhar limit, which is about 1.4 solar masses. Exceeding this limit means the white dwarf can go supernova.
The resulting explosion produces Type 1a supernovae, which are a useful measurement tool for astronomers because their light output is constant from event to event. By comparing Type 1a supernovae at different distances and observing how their light is redshifted by the expansion of the universe, a value for the expansion rate of the universe (the Hubble constant) can be obtained. This value can be used to understand the influence of dark energy on the cosmos at different times.
The story is significant because it was the study of 50 Type 1a supernovae in 1998 that first led astronomers to suspect the existence of dark energy.
Type 1a supernova SN 2011fe, discovered in the Pinwheel Galaxy. BJ Fulton/Palomar Transient Factory
Since then, astronomers have observed another 2,000 Type 1a supernovae using different telescopes. The new Union3 project removes any differences between observations caused by different astronomical instruments, such as the drift of telescope filters over time, and compiles the largest standardized data set of Type 1a supernovae ever.
Union3 contains data on 2,087 supernovae from 24 different datasets spanning 7 billion years of cosmic time. It is based on the 557 supernovae catalogued in the original Union2 dataset.
Union3’s analysis does appear to confirm DESI’s findings that dark energy is weakening over time, but the results are not yet conclusive.
The team’s Type 1a supernova dataset will be expanded by adding three more datasets in 2026. Two of these will contain data on high-redshift supernovae observed at large distances, and one will contain data on more local, low-redshift supernovae. This should help better calibrate the new results, the researchers say.
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