Gamma-ray bursts (GRBs) are flashes of gamma rays from extremely energetic explosions. They have been seen in distant galaxies. They are the most luminous electromagnetic events known to occur in the universe.
Bursts can last from milliseconds to several minutes, although a typical burst lasts a few seconds. The initial burst is usually followed by a longer-lived 'afterglow' emitted at longer wavelengths (X-ray, ultraviolet, visible light, infrared and radio waves).
Most GRBs are a narrow beam of intense radiation released during a supernova, as a huge rapidly spinning star collapses to form a black hole. A subclass of GRBs (the 'short' bursts) seem to come from a different process, perhaps the merger of binary neutron stars.
The sources of most GRBs are billions of light years away from Earth. This suggests the explosions are extremely energetic: a typical burst releases as much energy in a few seconds as the Sun will in its entire 10 billion year lifetime. They are very rare (a few per galaxy per million years).
All observed GRBs have come from outside the Milky Way galaxy. Similar phenomena, soft gamma repeater flares, are associated with magnetars within the Milky Way. It has been suggested that a gamma-ray burst in the Milky Way could cause a mass extinction on Earth. No such case is known.
Gamma-ray bursts were first observed in the late 1960s by the U.S. Vela satellites, which were built to detect gamma radiation pulses emitted by nuclear weapons tested in space.
On July 2, 1967, at 14:19 UTC, the Vela 4 and Vela 3 satellites detected a flash of gamma radiation unlike any known nuclear weapons signature. Uncertain what had happened but not considering the matter particularly urgent, the team at the Los Alamos Scientific Laboratory filed the data away for investigation.
By analyzing the different arrival times of the bursts as detected by different satellites, the team was able to determine rough estimates for the sky positions of sixteen bursts and definitively rule out a terrestrial or solar origin. The discovery was published in 1973.
Most observed events last longer than two seconds and are classified as long gamma-ray bursts. They have been studied in much greater detail than their short counterparts. Almost every well-studied long gamma-ray burst has been associated with a rapidly star-forming galaxy and in many cases a core-collapse supernova as well. This links long GRBs with the deaths of massive stars. Long GRB afterglow observations at high redshift (great distances) also suggest GRBs originate in star-forming regions. This is because observing distant galaxies is to look back in time to galaxies at an earlier stage.
Gamma-ray bursts are thought to be highly focused explosions, with most of the explosion energy in a narrow relativistic jet travelling at speeds over 99.995% of the speed of light.
The approximate angular width of the jet (that is, the degree of beaming) can be estimated directly by observing "jet breaks" in afterglow light curves: a time after which the slowly-decaying afterglow begins to fade suddenly, as the jet slows down and can no longer beam its radiation so effectively. Observations suggest significant variation in the jet angle from between 2 and 20 degrees.
Because their energy is strongly beamed (very narrow), the gamma rays emitted by most bursts miss the Earth and are never detected. When a gamma-ray burst is pointed towards Earth, the focusing of its energy along a relatively narrow beam causes the burst to appear much brighter than it would have been were its energy emitted spherically. When this effect is taken into account, typical gamma-ray bursts are observed to have a true energy release of about 10 J, or about 1/2000 of a Solar mass energy equivalent.
This is comparable to the energy released in a bright type Ib/c supernova (sometimes called a 'hypernova'). Very bright supernovae have been seen at the position of some of the nearest GRBs.
Philosophy of religion
Philosophy of religion is a branch of philosophy. Religions, and religious beliefs can manifest themselves in different ways. Philosophy of religion looks into explaining certain answers to questions of religion using understanding. It is also looks into different ways religions are practiced and their importance for the everyday lives of the people practicing them. Other domains of it include criticism and analysis of religious texts using philosophy of language.
According to Winfried Löffler, philiosphers of religion can be grouped as follows. Many of the philosophers mentioned belong to more than one group:
Philosophy of religion also looks at more practical matters like defining the features that make up a religion. There are two main schools of thought. The one called Essentialist says that all religions have a common"essence". The following have been proposed:
The problem with this is that using only these definitions leas to a common "philiosphy of religion" that is harly usable for studies. The other approach (called "functional") tries to counter this: Rather than trying to get an "abstract idea" of religion, it looks at the use or function religion has in the live of people or societies. Among the things mentioned are that religions help keep a psychological equilibrium and that they provide a certain amount of stability to a society. Thinkers with this opion include Karl Marx, Émile Durkheim, Bronisław Malinowski and Talcott Parsons. Critics of these theories say that such explanations often go against common sense, as religions can also have the popposite effect to that mentioned.
Other topics include arguments for the existence of God, the problem of evil, divine attributes and the relationship between science and religion.
Important philosophers of religion include Thomas Aquinas, Augustine and Alvin Plantinga. Philosophers of religion can be religious or non-religious
Rough-skinned newt
The rough-skinned newt ("Taricha granulosa") is a North American newt known for its strong poison.
Juveniles live on land for four or five years after metamorphosis. Adults are amphibious, and live in water and on land. Eggs are laid in water. They can be found especially after there has been a lot of rain.
Many newts make toxin in their skin to avoid predation, but the rough-skinned newt is especially poisonous. Toxicity is generally experienced only if the newt feels threatened, although sometimes skin irritation can be experienced after touching it.
The toxin that the rough-skinned newt makes can either paralyze or kill a human. Recently, a drunk 29-year-old man in Coos Bay, Oregon, died after swallowing a rough-skinned newt for a dare.
Throughout much of the newt’s range, the common garter snake ("Thamnophis sirtalis") is resistant to the newt's toxin. In several populations, these snakes successfully prey upon the newts. Toxin resistant garter snakes are the only known animals today that can eat a "T. granulosa" newt and survive.
This is an example of co-evolution. The snake’s resistance to the toxin has resulted in a selective pressure that favours newts which produce more potent levels of toxin. Increases in newt toxicity then apply a selective pressure favouring snakes with mutations conferring even greater resistance.
This cycle of a predator and prey co-evolving is sometimes called an evolutionary arms race. In this case it results in the newts producing levels of toxin far in excess of what is needed to kill any other conceivable predator.
Toxic animals usually warn predators that they are not good food. There's no point in being toxic unless it helps survival and reproduction. The underside of these newts is vividly coloured a yellow-orange. When a threat appears, the newt curls up its tail and lifts its head to show the warning colour. This can be seen in photographs.