Why does dark matter exist

Yet, there is matter in the universe that does not emit light in any part of the electro-magnetic spectrum, which means that we cannot observe it with our telescopes. This unique property makes it impossible to observe these types of matter, so scientists call it dark matter. Some scientists, specifically astrophysicists , spend a great deal of time generating theories about what dark matter could be.

Scientists know that dark matter does not emit light from any part of the electro-magnetic spectrum, but dark matter has been observed to be influenced by gravity. Astrophysicists are still unsure what dark matter is, exactly.

However, they know what dark matter is not, by observing the way it behaves compared to other materials. This means that there is four times more dark matter compared to regular matter! If dark matter is so difficult to observe, why do scientists believe it actually exists?

The evidence to support the existence of dark matter is extensive, and we will explore three main examples in the following sections. The first type of evidence supporting the existence of dark matter has to do with the way dark matter affects the movement of celestial bodies.

In our solar system, almost all of the mass is in the sun. The innermost planets like Mercury and Venus orbit the sun the fastest. As the distance from the sun increases, the speed at which planets move decreases. This is because there is less gravitational pull from the sun on planets farther out and, to keep from spiraling into or away from the sun, they must move slower.

We can apply a similar analogy to galaxies. If we assume that the bright part of a galaxy shows where most of the mass is, then most of the mass is near the center, and at the dim edge of a galaxy there should not be much mass. Therefore, objects orbiting far from the center of the galaxy should move slower than objects closer to the center, just like the planets in our solar system.

To test this hypothesis, scientists recorded the incoming light from a distant spiral galaxy our home galaxy, the Milky Way, is also considered a spiral galaxy and plotted the velocities of the stars vs.

Scientists discovered that the stars were not behaving in the way anticipated. They found that the stars farther away from the center were moving much faster than predicted Figure 1. The only way this is possible is if there is more mass in the outer parts of galaxies than we can observe.

They think something we have yet to detect directly is giving these galaxies extra mass, generating the extra gravity they need to stay intact. Unlike normal matter, dark matter does not interact with the electromagnetic force. This means it does not absorb, reflect or emit light, making it extremely hard to spot. In fact, researchers have been able to infer the existence of dark matter only from the gravitational effect it seems to have on visible matter.

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We can tell that dark matter exists and even infer some of its properties by observing how it affects the matter and light we can observe, particularly in large-scale astrophysical environments. But the fact that dark matter has eluded direct, laboratory detection thus far means that a number of its properties remain open questions.

Here are five things we know about dark matter, along with five that we don't, as we probe the limits of our scientific frontiers. The heart of the Omega nebula is highlighted by ionized gas, brilliant new, blue, massive stars, and If normal matter could take on the form of gas, dust, plasma, black holes, or other non-luminous sources, many have hoped that it could be responsible for all the 'missing mass' without the need for dark matter.

However, observations indicate otherwise. Dark matter is not simply normal matter that we cannot detect. This is something that's completely known. Dark matter cannot be:. We have a suite of evidence that rules out that possibility.

Based on the earliest, most pristine clouds of gas we've ever detected, we can measure how much hydrogen, deuterium, helium-3, helium-4, and lithium-7 the Universe was born with shortly after the Big Bang. These measurements determine exactly how much normal matter the Universe was born with, and that value is only one-sixth the needed amount of total mass.

The remaining five-sixths, therefore, must be something else entirely: dark matter. The dark matter structures which form in the Universe left and the visible galactic structures Dark matter must be cold in nature. In theory, whatever hitherto undiscovered particle is responsible for dark matter could have any mass at all, and could have been created moving quickly or slowly or not at all, relative to the speed of light.

But if dark matter moved quickly, its properties would suppress the formation of structure on small scales, leading to different structures than what we can observe. In particular, we have three lines of observational evidence that constrain the temperature of dark matter: the gravitational lensing of quadruply-lensed quasars , absorption features along the line-of-sight to distant objects, and tidal streams in the Milky Way's vicinity.

All three of these teach us the same thing: dark matter must either be quite heavy or must have been born slow-moving. In other words, dark matter must have been "cold" even in the very early stages of the Universe, as opposed to hot or warm. A new particle must be directly and unambiguously detected before it's accepted as being 'real.

Dark matter must not interact very much with itself, with light, or with normal matter. There's no doubt that if dark matter exists, there must have been a pathway for its creation in the young Universe. However, whatever that pathway was, those interactions are no longer occurring and haven't occurred with great abundances in a very long time. Direct detection experiments haven't revealed dark matter, constraining its possible mass and cross-section.

It doesn't absorb or blur distant starlight, restricting its interactions with light. It doesn't annihilate with itself above a certain threshold, otherwise a large and diffuse gamma-ray signal would be seen at the centers of galaxies. If we hope to detect it directly, we'll have to push these limits even further, and even then, there's no guarantee of a positive signal. Dark matter might not interact at all in these fashions.

Only approximately stars are present in the entirety of dwarf galaxies Segue 1 and Segue 3,