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first_black_holes.html
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first_black_holes.html
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<!DOCTYPE html>
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<meta name="description" content="The site is intended as a free educational resource about the frontiers of galaxy formation." />
<meta name="keywords" content="black holes, first black holes, primordial black holes, early universe, cosmic dawn, first galaxies, first stars, first black holes, cosmology" />
<meta name="author" content="Erika Hoffman" />
<title>First Black Holes - Cosmic Dark to Dawn</title>
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<div class="page_title">THE FIRST <br /> BLACK HOLES</div>
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When the first stars ran out of fuel, their lives as stars ended. But, for many of them, their stories continued as black holes – objects with such intense gravity that even light could not escape them. Such remnant black holes are uncommon in today’s galaxies, but the very massive first stars probably formed black holes at much greater rates. Alternatively, black holes may have formed directly in some unusual environments. In either case, the black holes sit inside of dark matter clumps that continue to grow as matter falls onto them. Some of this matter flowed into the black hole, where the intense gravity of the black hole captured it. The matter heated up as it fell onto the black hole, radiating intense energy – as powerful as X-rays – into the universe around them.
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An artist's conception of the most primitive <i>supermassive black holes</i> known, at the core of a young, star-rich galaxy.
<br />Image Credit: <a href="https://images.nasa.gov/details-PIA12966" target="_blank" rel="noopener noreferrer">JPL</a>
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<a href="light_fills_the_universe.html" style="float: right;"> Next: Light Fills the Universe </a>
<a href="first_stars.html">Previous: The First Stars </a>
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<h1>What is a black hole?</h1>
<p>
A <i>black hole</i> is a concentration of matter so dense that its gravity prevents anything – even light – from escaping. In principle, black holes can be any size: even a tiny amount of matter can form a black hole if it is compressed into a small enough region. But astronomical black holes typically come in two varieties: black holes ten or so times as massive as the Sun and black holes millions or billions of times more massive than the Sun. The first type forms after stars run out of fuel; the origin of the latter is unknown, but they appear to be common near the centers of galaxies. (Our own Milky Way has a black hole at its center that is about four million times more massive than the Sun.)
</p>
<p class="img_cred_body">
Image: Artist concept illustrates a <i>quasar</i>, or feeding black hole
<br />Credit: <a href="https://images.nasa.gov/details-PIA16114" target="_blank" rel="noopener noreferrer">JPL</a>
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<h1>How did the first black holes form?</h1>
<p>
The origin of the first black holes is not yet known - after all, these sources have not yet been observed! But, because the first stars were very likely many times more massive than the Sun, many of them likely collapsed into black holes when they consumed their fuel. Black holes could have formed in other ways, though: in exceptional circumstances, early gas clouds may not have collapsed rapidly into stars but may have condensed much more slowly - and directly - into black holes up to a million times more massive than the Sun. Such black holes were likely very rare, but they may still have had enormous impacts on their surroundings.
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<p class="img_cred_body">
Image: A depiction of the gas collapsing in the time around the first stars, created with supercomputers.
<br />Credit: <a href="https://tomabel.org/Home/Visualization/Pages/The_First_Stars_and_Galaxies.html" target="_blank" rel="noopener noreferrer">Tom Abel and Ralf Kähler</a>
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<h1>How do the first black holes grow?</h1>
<p>
Black holes are very simple objects: in an astronomical environment, their only qualities are their total mass and their spin. Because they still exert gravity, they will continue to <i>accrete</i> any normal matter that comes too close. This matter cannot escape, so the black hole grows – making its gravity even stronger! However, black holes can only grow if they are surrounded by gas – the rates at which most large black holes grow likely varies strongly over time, depending on their local environment, and the fraction of time that these very early black holes can accrete gas and grow is currently unknown.
</p>
<p class="img_cred_body">
Image: This artist's conception shows a supermassive black hole at the center of a remote galaxy digesting the remnants of a star.
<br />Credit: <a href="https://images.nasa.gov/details-PIA01884" target="_blank" rel="noopener noreferrer">JPL</a>
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<div class="in_text_image_right_7" style="background-image: url(images/accretion_disk.jpg); background-size: contain;"></div>
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<h1>Why do the environments of black holes radiate so much energy?</h1>
<p>
We have already seen that no matter or energy can escape black holes, so it may seem surprising that they are amongst the most <i>luminous</i> objects in the Universe! The key is that, although light cannot escape the black hole itself, it can escape the incredibly hot environments of some black holes. As a gas stream falls toward a black hole, it collides with other streams. The friction of such collisions heats up the gas, which can reach millions of degrees Celsius. The gas eventually collects into a disk, where it slowly spirals into the black hole. The hot, dense gas in the disk radiates an enormous amount of energy, including not just visible and <i>ultraviolet light</i> but even <i>X-rays</i>. These X-rays may have important implications for the surrounding Universe, but their prevalence will depend upon the fraction of time that black holes spend accreting gas.
</p>
<p class="img_cred_body">
Image: Artist's conception of a bright black hole <i>accretion disk</i>.
<br />Credit: <a href="https://images.nasa.gov/details-PIA20912" target="_blank" rel="noopener noreferrer">JPL</a>
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<h1>Which telescopes are trying to observe this?</h1>
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<div class="tiny_text">The Hydrogen Epoch of Reionization Array (HERA)</div>
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<p>Although these black holes produce X-rays and other intense radiation as they grow, they are so faint and distant that there is little hope of observing these sources directly in the foreseeable future. Instead, we hope to use low-frequency radio telescopes to measure their properties indirectly. </p>
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<! VOCAB !>
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<h2><a href="glossary.html">Vocab</a></h2>
<ul>
<li>Black Hole </li>
<li>Supermassive Black Hole </li>
<li>Quasar</li>
<li>Accretion </li>
<li>Luminosity</li>
<li>Ultraviolet Light </li>
<li>X-Rays </li>
<li>Accretion Disk</li>
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<a href="light_fills_the_universe.html" style="float: right;"> Next: Light Fills the Universe </a>
<a href="first_stars.html">Previous: The First Stars </a>
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<h1>Want to learn more?</h1>
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<li><a href="https://www.scientificamerican.com/article/the-puzzle-of-the-first-black-holes/" target="_blank" rel="noopener noreferrer">This article</a> describes how the formation of the first black holes leads to much larger black holes later on.</li>
<li><a href="https://www.popsci.com/black-hole-early-universe-stars/" target="_blank" rel="noopener noreferrer">This article</a> describes alternative ways in which the first black holes may have formed.</li>
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<br />Content and supervision by Professor Steven Furlanetto, website design by Erika Hoffman, funding and support from NASA NESS, NSF, & UCLA Physics and Astronomy.
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