🗊Презентация Possible fate of the universe

Possible Fate of the Universe

Chapter 16, Dark Matter, Dark Energy, and the Fate of the Universe If we know how much matter we have in the universe, then we can predict how the universe is going to evolve in the future… In our effort to measure the total mass of the universe and trying to determine how the universe is going to evolve, we have come to some surprising conclusions, that is, most of the mass of the universe are in the form of dark matter, and that there is an unknown force pushing the expansion of the universe in an ever-increasing rate. This unknown force is what astronomers refer to as the dark energy of the universe. In this chapter, we will examine the evidences supporting these conclusions, and look into… What is dark matter and dark energy? The fate of the universe

Dark Matter and Dark Energy Definitions… Dark Matter Dark matter is the name given to mass that we infer to exist through its gravitational effects but that emits no detectable radiation. Dark Energy Dark energy is the name given to an unseen influence that may be causing the expansion of the universe to accelerate with time. .

How do we measure the mass of Milky Way, or other galaxies?

The Rotation Curve of the Milky Way Galaxy

What Does the Flat Rotation Curve of the Milky Way Tell Us? Let’s first look at the rotation curves of a rigid body and a system with concentrated mass…

What Does the Flat Rotation Curve of the Milky Way Tell Us? The flat rotation curve of the Milky Way Galaxy implies that… The mass of the Milky Way is not concentrated at the center of the galaxy.. The mass enclosed in a sphere increases as we increase the radius of the sphere… The mass in a sphere inside the Sun’s orbit contains about 100 billion times the mass of the Sun. The mass in a sphere twice the size of the Sun’s orbit contains twice as much mass (200 billion Msun). Most of our galaxy’s mass lies well beyond our Sun, tens of thousands of light-years from the galactic center most of this mass is located in the spherical halo that surrounds the disk of our galaxy, and that the total amount of this mass might be 10 times the total mass of all the stars in the disk However, very little light is detected from these region!

The Rotation Curve of the Spiral Galaxies

Dark Matter in Spiral Galaxies All observations of the mass in spiral galaxies suggest that The majority of the masses in spiral galaxies are contained in a spherical halo that surrounds the disk of our galaxy, and 90% of the mass of the spiral galaxies do not emit light. They are DARK MATTER! Only about 10% of the mass in the spiral galaxies are in luminous form concentrated in the disk of the galaxies…

Dark Matter in Elliptical Galaxies We cannot measure the rotation rate of stars in Elliptical galaxies like we do with the spirals, because stars in elliptical galaxies do not rotate around the center in any organized way…However, At any particular location, some stars will be moving toward us, some will be moving away from us, while some will be moving perpendicular to the line-of-sight. This ‘random’ motion results in a broadened absorption spectrum – how large this broadening is can be used to measure their orbital speed.

Measuring the Mass of Galaxy Clusters The mass of cluster of galaxies can be measured by three different methods… Orbits of Galaxies in Cluster Hot Gas in Clusters Gravitational Lensing Effect The first method is obviously the application of the Newtonian dynamics methods (Kepler’s Third Law of Planet Motion)…

X-ray Observation of Intercluster Medium

Gravitational Lensing Effect

Results of Mass Measurements

What is Dark Matter?

Is Dark Matter Real? Do we really need dark matter to explain the observed rotation curves in galaxies? Remember Ether? This is our historical dark matter that was proven to be not in existence. In 19th century, physicists hypothesized on the existence of a omnipresence medium called Ether to carry the propagation of light! Recall that measurement of galactic mass are based on the assumptions that The strength of gravity is given by Newton’s Law of Gravity. The stars and gases used to measure the rotation of the galaxies are in bound orbits. What if… Newton’s theory of gravity is not correct at very large distance? Newton’s law has only been tested to a distance at the order of the size of the solar system… We don’t know how gravity behave in quantum mechanical scale either… Keep an Open Mind!

Possible Fate of the Universe

Evidence of the Acceleration of the Galaxies

Supernovae from Distant Galaxies These snapshots, taken by NASA's Hubble Space Telescope, reveal five supernovae, or exploding stars, and their host galaxies. The arrows in the top row of images point to the supernovae. The bottom row shows the host galaxies before or after the stars exploded. The supernovae exploded between 3.5 and 10 billion years ago. http://imagine.gsfc.nasa.gov/docs/features/news/news_d.html

Dark Energy and the Cosmological Constant