"Yep, however it only happens in Gym Stadiums or special pokemon den as that where the energy particle are strongest, though I hear that they were meteor that fell from the sky during an incident known as the Darkest Day. 
Some pokemon have Gigantamax form which are more powerful then Dynamax. Off the top my head I know that, Charizard, Dreadnaw, Alacreami, Centascorch, Blastose, Venaisaur and the Galar starters final evolutions have one. The current Champion has a Charizard that can do it, but you also need one of these as well" she said before rummaging though her bag before pulling out a dark purple band with a crystal within it. 

"This is called a Dynamax band, it's the only way you can make your pokemon Dynamax, however it can only be used in the Gym Stadiums which have protective windows protecting the spectators since it's always a mass event the gym battles. Dynamax dens are underground battle arenas where you will always find a Dynamaxed pokemon, however it's often advised to go in as a team of 4 as those wild pokemon are uber powerful when Dynamaxed" she told him as she invited him to walk with her back to the stadium to see the next battle update.