The Solar System was created 4.5 billion years ago, when the a cloud of molecular gas collapsed to form a proto-star—the star that which we today call the Sun. Along with the formation of the proto-star is the creation of an accretion disk around the star, which eventually coalesced to form the planets of the solar system.
The Nieves Observatory presents
A Brief Guide to Astronomical Objects
By Jerrick Wee
The Solar System
The celestial bodies are among the brightest objects in the night sky, and many can be seen with the naked eye. The moon tops the list, and is followed by the five brightest planets in the solar system—in order of brightness: Venus (-4.3 mag), Jupiter (-2.2 mag), Mercury (0.08 mag) Mars (0.83 mag), and Saturn (1.43 mag).
These five planets are known since ancient times for their peculiar movements through the night sky. Because they are, unlike stars, not fixed in position in the night sky, the ancient Greeks called them planētai, or wanderers, from which the term “planet” is derived.
A nebula (Latin for “cloud”) is an interstellar cloud of dust and gas. Some nebulae are created by cataclysmic events, such as the death and explosion of a massive star, that throw out gas and dust into the area. These powerful, destructive events leave behind a remnant that continues to glow from the residual heat of the explosion (see Crab nebula). Other nebulae are formed by the cooling and condensation of existing material in the interstellar medium.
Many nebulae are star-forming regions, and are also known as stellar nurseries. Stars are born when the giant clouds of gas in the nebula clump up and accrete matter till they collapses under their own weight, igniting a nuclear fusion from the accreted hydrogen. New, massive stars ionize the surrounding gas in the nebula, and render the nebula visible at optical wavelengths.
Famous and interesting nebulae
(Right: Mosaic from multiple images taken with the Hubble Space Telescope; colors resemble but are not true to the eye)
(Right: Image mosaic of Visible, H-alpha, and near-IR bands from the Hubble)
(Right: Image by the Hubble)
No stars are born alone. They are usually formed together in a star cluster—a group of stars that are bounded gravitationally. There are two kinds of star clusters: globular clusters and open clusters. Globular clusters are dense groupings of numerous stars that are spherically distributed (see Omega Centauri). Open clusters, on the other hand, are loosely bound together and tend to be young, bright stars. Over time, open clusters disperse to become individual stars.
Star clusters are important for distance calibration in astronomy, and are especially useful when stars in a cluster are plotted on a Hertzprung-Russell (HR) diagram. As we can compare the position of the main-sequence for different clusters, this main-sequence fitting allows us to determine the distance of different kinds of clusters through the distance modulus.
Famous and interesting star clusters
The Milky Way—that is, our Galaxy—was once considered to be all there is to the Universe. Everything we can see in the sky was considered part of the Milky Way; there is no “outside” of our Galaxy. We could see other celestial objects that we know today are other galaxies, such as the Andromeda Galaxy, but because they look like bodies of dust and clouds, they were thought be one of the many nebulae in our Galaxy.
Better telescopes eventually allow astronomers to see that galaxies are made of huge agglomerations of stars and are categorically distinct from nebulae. In 20th century, with even better telescopic evidence and distance calibration techniques, we learn that these “nebulae” are in fact distant galaxies themselves, whole different worlds on their own.
Each galaxy contains its own innumerable stars, its own countless nebulae, star clusters, and planets. It is believed that a supermassive black hole lies at the center of every galaxy. Morphologically, galaxies are thought to start out as elliptical galaxies and over time become spiral galaxies. However, there are some galaxies that do not conform to this galactic evolution, such as irregular galaxies and ring galaxies (see Hoag’s Object).
Once a topic of intense speculation, exoplanets—planets that orbit other stars—are now a scientific certainty. The first exoplanet, 51 Pegasi b, is a Jupiter-like exoplanet so close to its host star that it orbits the star in just 4 days. These “Hot Jupiters” are non-existent in the Solar System, and are now known to be relatively common in the Galaxy. More interestingly, we have also found Earth-like exoplanets in the habitable zone of their host stars with water in their atmosphere. This opens up the possibly for alien life similar to that of Earth, a domain of study belonging to astrobiology.
There are various ways that we can detect these alien worlds. The first method used is the radial-velocity method, where the gravitational influence of an exoplanet is strong enough to induce a detectable motion in its host star. Another more widely-used method today is transit photometry, where an exoplanet partially obscures the brightness of its host star whenever it moves in front of the star in our line of sight from Earth. The transit method can be performed at our very own Nieves Observatory (see photometry tutorial).
A white dwarf is made of electron-generate matter and is prevented from further collapse due to the pressure from fast-moving electrons on its surface. These objects are roughly the size of Earth and have a mass limit of 1.4 solar masses—any more mass and the electrons will not be able to sustain the pressure, causing them to go supernova.
Neutron stars are about the densest objects there are in the Universe, almost as dense as an atomic nucleus. They have a mass between 1.4 and 3 solar masses, but are only about 20km in diameter. Neutrons stars also have powerful magnetic fields that induces powerful beams of radiation around its magnetic pole. When oriented in the direction towards Earth, we observe these regular pulses of radiation as the neutron star spins about its axis. These kind of neutron stars are also known as pulsars.
Despite its name, black holes are not perfectly black. They do emit radiation through a mechanism known as Hawking's radiation. We can also observe black holes, albeit indirectly, through from their interaction with their surroundings. Active black holes at the center of galaxies accelerate matter near its event horizon and spew them out as relativistic jets occasionally. Black holes also heat the material around them, providing themselves with a ring of luminous gas as we see in the picture of the black hole in M87 on the right, taken by the Event Horizon Telescope.
Stars are often described by astrophysicists as if they are living things: they are born in nurseries (nebulae); metabolises food (stellar nucleosynthesis); attain adulthood (main sequence); become elderly and cranky (giant phase); and eventually die (planetary nebula or supernova). Like living things, when stars die, they too leave behind corpses. Depending on the initial mass of the star, stars leave behind different kinds of stellar corpses: white dwarfs, neutron stars, or black holes.
Stellar corpses are the most extreme objects in the Universe, pushing the boundaries of our understanding of physics the more we study them. For example, white dwarfs and neutron stars are made of a little-studied, exotic substance called degenerate matter. And because of our conflicting understanding of what happens when something extremely massive occupies an infinitely small space, the mechanics at the center of a black hole is a piece of knowledge hitherto forbidden to the human intellect.
High Energy Phenomenon
Type Ia Supernovae
Type Ia supernovae produces a consistent peak brightness because of this fixed critical mass at which a white dwarf will explode. This makes them excellent candidates as standard candles to measure distances in, and ultimately the age of, the Universe. The explosion also creates abundantly the isotope nickel-56 which decays to cobalt-56 and finally to the stable iron-56. Most of the iron in the Universe is created from Type Ia supernovae.
Kilonova produces almost all of the extra-heavy and extra-rare elements in the Universe, such as gold, silver, and platinum. A merger between a neutron star and a black hole is also called a kilonova.
Black Hole Mergers
When we say high energy in space, we really do mean it. An explosion of a white dwarf, called a type Ia supernova, shines with the intensity of 10 billion suns and produces an amount of energy equivalent to the amount that the Sun produces in its lifetime.
A black hole merger generates no light even though the energy output is much greater than that of a supernova. Most of the energy is released in the form of gravitational waves, a disruption of the fabric of spacetime propagating through the cosmos.
Most interesting are the phenomena that release energy in various forms. A kilonova—the merger of two neutron stars—produces both detectable gravitational waves and electromagnetic radiation, which allows astronomers to study such a phenomenon with both optical telescopes and gravitational wave observatories.
Multi-messenger astronomy is currently one of the newest fields in astronomy, and telescopes that can observe these transients (such as the Nieves Observatory) are well-positioned to advance the frontiers of astronomy and human knowledge.
© 2020 Nieves Observatory at Soka University of America.
With media resources from NASA & ESO/Hubble.