Cosmology and Dark Matter | ELT

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</div> </nav> <div class="container-fluid container-dark container-tight position-relative"> <img class="d-block h-100 w-100" src="https://cdn.eso.org/images/banner1920/subheader-science-cosmology.jpg" /> <div class="position-absolute science-header-textblock" > <div class="d-flex flex-column justify-content-around h-100"> <div class="header-title">Cosmology and Dark Matter</div> <div class="d-none d-xl-block header-subtitle"><p>What we see around us — the planets, stars and dust in between them — makes up just 5% of the Universe.</p></div> <div class="d-none d-xxl-block header-description"> <p>The rest is invisible dark matter and a mysterious dark energy that is thought to be causing the Universe to expand faster and faster. When this accelerating expansion was discovered in the 1990s, it completely challenged what we thought we knew about the laws of the Universe. The ELT will finally give us a way to search for, identify and ultimately characterise the new physics that is waiting to be unearthed.</p> </div> <div class="d-block header-quick-links"> <div>Quick Links:</div> <div class="instrument-link-color"> <a class="instrument-link-color instrument-link" href="#watching-the-universe-expand">Cosmology</a> | <a class="instrument-link-color instrument-link" href="#dark-matter">Dark matter</a> </div> </div> </div> </div> </div> <div class="container-fluid container-light nutshell"> <div class="container-paragraph section-title-paragraph d-flex align-items-center justify-content-between"> <div class="">In a nutshell</div>                      <div class="d-flex"> <a class="share-social-media-link share-social-media-icons" href="https://www.facebook.com/sharer/sharer.php?u=https://elt.eso.org/" title="Share on Facebook" target="_blank" rel="noopener noreferrer"> <img src="/public/archives/djp/elt-assets/img/social-media/icon_share_1.png" alt="Share on Facebook"> </a> <a class="share-social-media-link share-social-media-icons" href="https://twitter.com/intent/tweet?url=https://elt.eso.org/&text=&via=ESO" title="Share on X/Twitter" target="_blank" rel="noopener noreferrer"> <img src="/public/archives/djp/elt-assets/img/social-media/icon_share_2.png" alt"Share on X/Twitter"> </a> <span class="position-relative d-flex" style="" title="Share on Social Media"> <span class="share-social-media share-social-media-icons"> <img class="share-social-media" src="/public/archives/djp/elt-assets/img/social-media/icon_share_3.png" alt"Share on Social Media"> </span> <div class="position-absolute share-social-media-dropdown"> <div class="share-social-media-dropdown-icons"> <a class="share-social-media-link" href="https://www.facebook.com/sharer/sharer.php?u=https://elt.eso.org/" title="Share on Facebook" target="_blank" rel="noopener noreferrer"> <img src="/public/archives/djp/elt-assets/img/social-media/icon_share_1.png" alt="Share on Facebook"> <span class="share-social-media-dropdown-text">Share on Facebook</span> </a> <a class="share-social-media-link share-email" href="#" title="E-Mail"> <img src="/public/archives/djp/elt-assets/img/social-media/icon_share_5.png" alt="E-Mail"> <span class="share-social-media-dropdown-text">E-Mail</span> </a> <a class="share-social-media-link" href="https://twitter.com/intent/tweet?url=https://elt.eso.org/&text=&via=ESO" title="Share on X/Twitter" target="_blank" rel="noopener noreferrer"> <img src="/public/archives/djp/elt-assets/img/social-media/icon_share_2.png" alt"Share on X/Twitter"> <span class="share-social-media-dropdown-text">Share on X/Twitter</span> </a> <a href="#" class="share-social-media-link clipboard" title="Copy Link"> <img src="/public/archives/djp/elt-assets/img/social-media/icon_share_6.png" alt="Copy link"> <span class="share-social-media-dropdown-text">Copy Link</span> </a> <a class="share-social-media-link" href="https://www.linkedin.com/sharing/share-offsite/?url=https://elt.eso.org/" title="Share on LinkedIn" target="_blank" rel="noopener noreferrer"> <img src="/public/archives/djp/elt-assets/img/social-media/icon_share_4.png" alt="Share on LinkedIn"> <span class="share-social-media-dropdown-text">Share on LinkedIn</span> </a> </div> </div> </span> </div> </div> <div class="container-subtitle d-none d-xl-block d-xxl-none section-subtitle-paragraph-aftertitle"><p>The rest is invisible dark matter and a mysterious dark energy that is thought to be causing the Universe to expand faster and faster. When this accelerating expansion was discovered in the 1990s, it completely challenged what we thought we knew about the laws of the Universe. The ELT will finally give us a way to search for, identify and ultimately characterise the new physics that is waiting to be unearthed.</p></div> <div class="container-subtitle d-block d-xl-none section-subtitle-paragraph-aftertitle"><p>What we see around us — the planets, stars and dust in between them — makes up just 5% of the Universe.</p></div> <div class="container-paragraph d-block d-xl-none section-text-paragraph"><p>The rest is invisible dark matter and a mysterious dark energy that is thought to be causing the Universe to expand faster and faster. When this accelerating expansion was discovered in the 1990s, it completely challenged what we thought we knew about the laws of the Universe. The ELT will finally give us a way to search for, identify and ultimately characterise the new physics that is waiting to be unearthed.</p></div> <div class="container-paragraph section-text-paragraph"> <p>Galaxies rotate fast. So fast that the gravity generated by stars, dust and gas could not possibly hold them together. This led astronomers to believe that galaxies are surrounded by a halo of invisible dark matter, but despite being suggested almost 100 years ago, the nature of this dark matter remains enigmatic. The ELT will be able to peer at the dark matter halos around distant galaxies, to help us understand how much of each galaxy is made up of dark matter, and perhaps finally understand what exactly this strange substance is made of. </p> <p>Dark matter makes up around a quarter of the Universe, but the even more mysterious dark energy makes up about 70%. In the 1920s, astronomer Edwin Hubble made revolutionary observations that provided the first direct evidence that the Universe was expanding, or that other galaxies are moving away from us and away from each other. For a long time, this expansion was assumed to be slowing down due to the gravitational pull that all matter in the Universe exerts on all other matter. However, in the 1990s a team of astronomers made the shocking discovery that the expansion is actually accelerating. </p> <p>This discovery profoundly changed cosmology because it suggested that there is another component in the Universe that we cannot see, but that is acting against gravity and pushing space apart. We have named this component dark energy, but it remains a mystery. It suggests our theories of cosmology and particle physics are incomplete (or possibly incorrect) and that new physics is out there, waiting to be discovered. A key task for the next generation of astrophysical facilities is to search for, identify and ultimately characterise this new physics. </p> <p>Ironically, the simplest form of such a dark energy is the cosmological constant that was introduced by Einstein when he was trying to ensure that his theory of general relativity allowed for a non-expanding Universe, the accepted view at the time. As it happens, the theory of general relativity with the cosmological constant actually explains the accelerating expansion very well. Alternatively, it has been proposed that general relativity should be replaced with a modified theory of gravity, which would explain the accelerating expansion and the formation of structures in the early Universe by a different behaviour of gravity on the largest scales.</p> <p>The ELT will provide unique contributions towards deciding whether general relativity or a modified theory of galaxy best describes the expansion of the Universe, including testing the behaviour of gravity in unexplored regimes, as well as mapping the expansion history of the universe.</p> </div> </div> <div class="container-fluid container-light lightlinks"> <div class="row d-flex w-100 m-0 align-items-stretch" style="background-color: rgb(75, 92, 116);"> <div class="col-lg-6 p-0 position-relative"> <a href="#watching-the-universe-expand"> <img class="w-100" src="https://cdn.eso.org/images/banner1920/science-cosmology-watching.jpg" /> </a> <span class="position-absolute internal-menu-title"><a href="#watching-the-universe-expand">Cosmology: watching the Universe expand</a></span> </div> <div class="col-lg-6 pb-3 pt-3 d-flex align-items-center position-relative"> <div class="internal-menu-text"> <p style="text-align: left;">The ELT will revolutionise the way we measure the acceleration of the Universe allowing us to unravel the mysteries of dark energy.</p> </div> <div class="h-100 w-100 position-absolute d-flex align-items-end internal-menu-shape"> <div class="w-100 d-none d-lg-block"> <svg class="instrument-trapezoid internal-menu-trapezoid" viewBox="0 0 945 75" preserveAspectRatio="none" style="/* height: 75px; */"> <a href="/science/cosmodm/#watching-the-universe-expand"> <polygon points="0,0 260,0 340,67 945,67 945,75 0,75" /> </a> </svg> </div> </div> <div class="position-absolute d-none d-lg-flex align-items-center justify-content-center internal-menu-link internal-menu-trapezoid-link"> <a href="#watching-the-universe-expand" style="color: rgb(75, 92, 116);"> Read more </a> </div> </div> </div> <div class="row d-flex w-100 m-0 align-items-stretch" style="background-color: rgb(106, 73, 91);"> <div class="col-lg-6 pb-3 pt-3 d-flex align-items-center position-relative order-2 order-lg-1"> <div class="internal-menu-text"> <p style="text-align: left;">The ELT will also help us gather clues about the other component of the dark Universe, dark matter, by helping to measure the shape of dark matter halos.</p> </div> <div class="h-100 w-100 position-absolute d-flex align-items-end internal-menu-shape" > <div class="w-100 d-none d-lg-block"> <svg class="instrument-trapezoid internal-menu-trapezoid" viewBox="0 0 945 75" preserveAspectRatio="none" style="/* height: 75px; */"> <a href="/science/cosmodm/#dark-matter"> <polygon points="0,0 260,0 340,67 945,67 945,75 0,75" /> </a> </svg> </div> </div> <div class="position-absolute d-none d-lg-flex align-items-center justify-content-center internal-menu-link internal-menu-trapezoid-link" > <a href="#dark-matter" style="color: rgb(106, 73, 91);"> Read more </a> </div> </div> <div class="col-lg-6 p-0 position-relative order-1 order-lg-2"> <a href="#dark-matter"> <img class="w-100" src="https://cdn.eso.org/images/banner1920/science-cosmology-dark.jpg" /> </a> <span class="position-absolute internal-menu-title" ><a href="#dark-matter">Dark matter</a></span> </div> </div> </div> <a id="watching-the-universe-expand" class="anchor"></a> <div id="watching-the-universe-expand_" class="container-fluid container-light page-section"> <div class="container-paragraph section-title-paragraph">Cosmology: watching the Universe expand</div>  <div class="m-0 " style="padding-bottom: 1vw;"> <div class="row w-100 m-0"> <div class="col-lg-12 p-0 position-relative d-flex align-items-center order-lg-1 order-1" > <a href="https://www.eso.org/public/images/science-cosmology-banner1/" target="_blank" rel="noopener noreferrer" class="d-flex align-items-center justify-content-center w-100" > <img class="" style="width: 100%; " src="https://cdn.eso.org/images/original/science-cosmology-banner1.jpg" /> </a> </div> </div> </div>    <div class="container-heading"> <span class="section-heading-paragraph"><p>To understand our Universe we need to understand what’s driving its acceleration, which requires astronomers to determine the expansion history of the Universe. The ELT will revolutionise the way we measure the acceleration of the Universe allowing us to unravel the mysteries of dark energy.</p></span> </div> <div class="container-paragraph section-text-paragraph"> <p>Standard probes of the expansion of the Universe include weak gravitational lensing and the signature that light imprinted shortly after the Big Bang on today’s distribution of galaxies, and type Ia supernovas. The ELT will contribute to current efforts to measure the acceleration of the Universe by characterising high-redshift Type Ia supernovas identified by James Webb Space Telescope and other survey facilities. </p> <p>But the ESO telescope will also map the expansion history of the Universe using a whole different method, by watching the Universe expand in real time. </p> <p>Extracting information about the Universe’s expansion from standard probes relies on assumptions about the curvature of space, depends on the adopted cosmological model, and can only estimate the average expansion history over long time periods. A model-independent approach that measures the expansion rate directly was proposed as early as the 1960s, but limitations in technology have meant that astronomers have not been able to make such a measurement in practice. This approach is known as redshift drift, and is a method that offers a truly independent and unique approach to exploring the expansion history of the Universe. The redshift of the spectra of distant objects is an indication of the expansion of the Universe, so the change in this redshift over time is a measure of the change in the rate of expansion. However, the estimated size of this redshift drift over a decade is only about 10 cm/s. Such a signal is about 10–20 times smaller than today’s large telescopes can measure in such distant galaxies. The huge light-collecting area of the ELT, coupled with new developments in quantum optics to record ultrastable spectra, means that this amazing measurement now lies within reach. </p> <p>Astronomers will use the redshift drift method with the ELT’s <a href="/instrument/HIRES/">ANDES</a> instrument to determine the accelerating expansion of the Universe directly, thereby allowing us to quantify the nature of the dark energy responsible for the acceleration. Once a first epoch of observations is made, the redshift drift signal grows linearly with time. Hence, in the very long run (on the timescale of many decades) the redshift drift may well overtake the ability of other methods to constrain the expansion history of the Universe. </p> <p>Apart from the fundamental conceptual importance of directly observing the Universe’s expansion, the redshift drift provides a new and crucial consistency test of the assumptions of our theories of cosmology. Two other such tests that will be significantly improved by the ELT are measurements of the temperature of the cosmic microwave background radiation and the primordial abundances of light elements. </p> </div>  <div class="m-0 " style="padding-bottom: 1vw;"> <div class="row w-100 m-0"> <div class="col-lg-12 p-0 position-relative d-flex align-items-center order-lg-1 order-1" > <a href="https://www.eso.org/public/images/constrainig-power-redshiftdrift/" target="_blank" rel="noopener noreferrer" class="d-flex align-items-center justify-content-center w-100" > <img class="" style="width: 40%; border: 1px solid rgb(188, 189, 190);" src="https://cdn.eso.org/images/screen/constrainig-power-redshiftdrift.jpg" /> </a> </div>  <div class="col-lg-12 pt-3 d-block align-items-center order-lg-3 order-2 caption-text"> <p style="text-align: center;">Illustrating the constraining power of redshift drift measurements by the ELT for various cosmological models. Credit: Carlos Martins</p> </div> </div> </div>        </div> <a id="dark-matter" class="anchor"></a> <div id="dark-matter_" class="container-fluid container-light page-section"> <div class="container-paragraph section-title-paragraph">Dark matter</div>  <div class="m-0 " style="padding-bottom: 1vw;"> <div class="row w-100 m-0"> <div class="col-lg-12 p-0 position-relative d-flex align-items-center order-lg-1 order-1" > <a href="https://www.eso.org/public/images/eso1212c/" target="_blank" rel="noopener noreferrer" class="d-flex align-items-center justify-content-center w-100" > <img class="" style="width: 100%; " src="https://cdn.eso.org/images/original/science-cosmology-banner3.jpg" /> </a> </div> </div> </div>    <div class="container-heading"> <span class="section-heading-paragraph"><p>The ELT will also help us gather clues about the other component of the dark Universe, dark matter, by helping to measure the shape of dark matter halos.</p></span> </div> <div class="m-0 container-paragraph "> <div style="width: 33%;" class="d-none d-lg-flex flex-column align-items-center justify-content-between float-left mr-5 mb-3"> <div > <a href="https://www.eso.org/public/images/eso1217a/" target="_blank" rel="noopener noreferrer"><img class="w-100 d-block " style="" src="https://cdn.eso.org/images/screen/science-cosmology-eso1217a.jpg" /></a> <div class="px-3_ pt-3 pb-3 caption-text">Artist’s impression of the expected dark matter distribution around the Milky Way. Credit: ESO/L. Calçada</div> </div> </div> <div class="d-flex d-lg-none flex-column align-items-center justify-content-between w-100 mb-3"> <div > <a href="https://www.eso.org/public/images/eso1217a/" target="_blank" rel="noopener noreferrer"><img class="w-100 d-block " style="" src="https://cdn.eso.org/images/screen/science-cosmology-eso1217a.jpg" /></a> <div class="pt-3 pb-3 caption-text">Artist’s impression of the expected dark matter distribution around the Milky Way. Credit: ESO/L. Calçada</div> </div> </div> </div> <div class="container-paragraph float-text" > <span> <p>Astrophysical evidence for dark matter halos around galaxies first emerged in the 1930s with studies of galaxy rotation curves, which plot the velocities of stars and gas against their distance from the centre of their host galaxy. Such studies still play an important role today. They require high-resolution observations of kinematics from the inner parts of galaxies to it to constrain the distribution of baryonic <span style="color: #222222; font-family: arial, sans-serif; font-size: 16px;">—</span> or visible <span style="color: #222222; font-family: arial, sans-serif; font-size: 16px;">—</span> mass. At higher redshifts, rotation curves are not currently resolved enough to constrain the fraction of dark matter. However, using data from the <a href="https://www.eso.org/public/teles-instr/paranal-observatory/vlt/vlt-instr/sinfoni/">SINFONI</a> and <a href="https://www.eso.org/public/teles-instr/paranal-observatory/vlt/vlt-instr/kmos/">KMOS</a> instruments on <a href="https://www.eso.org/public/teles-instr/paranal-observatory/vlt/">ESO’s Very Large Telescope</a>, two recent studies tried to do this in the inner regions of distant galaxies using both seeing limited and adaptive optics-assisted observations, as well as stacking several images together to reduce noise. Their results point towards a low fraction of dark matter, a finding that is supported by the observation of decreasing rotation curves. However, these results remain controversial because the signal-to-noise ratio is low, and the spatial resolution is rather coarse. </p> <p>The ELT’s HARMONI will be the first instrument able to reach the spatial resolution needed to disentangle the visible matter distribution from the dark matter distribution for high redshift galaxies. Mass model distributions will provide the measurements of dark halo central density and core radius for galaxies in a redshift range that is not reachable with 8–10-metre class telescopes. Astronomers will be able to use the ELT to measure the shape of dark matter halos as a function of galaxy mass assembly history, cosmology, and environments. Detailed simulations show that HARMONI will be able to study spatially resolved kinematics with sufficient details and signal to noise ratio to perform mass models and recover the shape of dark matter halos down to stellar masses of 10<sup>9</sup> solar masses at redshift 1.4 and 10<sup>9.5</sup> solar masses at redshift 2.7 using the Hα line in just 2 hours of exposure. A multi-object spectrograph like the ELT’s MOSAIC instrument will allow us to expand the statistical sample of galaxies, as well as extending studies of rotation curves and dark matter profiles.</p> </span> </div> <div style="clear: both;"></div> </div> <footer class="container-fluid container-footer"> <div class="row d-flex align-items-center justify-content-between w-100"> <div class="col-12 col-lg-3 pb-3 pb-lg-0 d-flex align-items-center justify-content-center medium-light footer-item"> <a href="https:///www.eso.org/"><span class="esoblue">ESO</span></a> | ELT ©  <div id="current-year"> </div> <script> //Get Current year var today = new Date(); var year = today.getFullYear(); document.getElementById('current-year').innerHTML = `${year}`; </script> </div> <div class="col-12 col-lg-9 d-flex align-items-center justify-content-center medium-light footer-item"> <div class="text-center"> <a class="w-100" href="/credits/"><span class="medium-light footer-item">Credits</span></a>   |   <a class="w-100" href="mailto:information@eso.org"><span class="medium-light footer-item">Contact us</span></a>   |   <a class="w-100" href="https://www.eso.org/public/outreach/newsletters/"><span class="medium-light footer-item">Subscribe to ESO news</span></a>   |   <a class="w-100" href="https://www.cdn77.com/"><span class="medium-light footer-item">Accelerated by CDN77</span></a>   |   <a class="w-100" href="https://www.eso.org/public/about-eso/privacy/"><span class="medium-light footer-item">Terms & Conditions</span></a> </div> </div> </div> </footer> <input type='hidden' name='csrfmiddlewaretoken' value='zZyLbVVyzF6TVcZO7GkrQlG4t9dOBR4vHTozTYtgX9TCvXVeygUjp28E6N4TecU0' /> </body> </html>

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